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 $237.84   11.397%   $264.9466   $264.95   $264.95   $264.90  
  Purchase #2 $91.77   13.121%   $103.8111   $103.81   $103.80   $103.80  
  Purchase #3 $86.53   10.594%   $95.697   $95.70   $95.70   $95.70  
  Purchase #4 $207.46   6.797%   $221.5611   $221.56   $221.55   $221.60  
  Purchase #5 $129.37   4.302%   $134.9355   $134.94   $134.95   $134.90  
  Purchase #6 $163.60   6.531%   $174.2847   $174.28   $174.30   $174.30  
  Purchase #7 $23.27   7.237%   $24.954   $24.95   $24.95   $25.00  
  7 purchase totals = $939.84       $1,020.1900   $1,020.19   $1,020.20   $1,020.20