Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.79   8.712%   $262.8547   $262.85   $262.85   $262.90  
  Purchase #2 $145.98   6.150%   $154.9578   $154.96   $154.95   $155.00  
  Purchase #3 $187.98   12.645%   $211.7501   $211.75   $211.75   $211.80  
  Purchase #4 $225.31   11.133%   $250.3938   $250.39   $250.40   $250.40  
  Purchase #5 $165.66   11.652%   $184.9627   $184.96   $184.95   $185.00  
  Purchase #6 $227.88   6.861%   $243.5148   $243.51   $243.50   $243.50  
  Purchase #7 $152.51   12.782%   $172.0038   $172.00   $172.00   $172.00  
  7 purchase totals = $1,347.11       $1,480.4377   $1,480.42   $1,480.40   $1,480.60