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 $60.56   11.166%   $67.3221   $67.32   $67.30   $67.30  
  Purchase #2 $187.27   9.237%   $204.5681   $204.57   $204.55   $204.60  
  Purchase #3 $83.73   4.840%   $87.7825   $87.78   $87.80   $87.80  
  Purchase #4 $202.91   11.374%   $225.989   $225.99   $226.00   $226.00  
  Purchase #5 $211.62   11.452%   $235.8547   $235.85   $235.85   $235.90  
  Purchase #6 $230.69   5.861%   $244.2107   $244.21   $244.20   $244.20  
  Purchase #7 $229.50   10.705%   $254.068   $254.07   $254.05   $254.10  
  7 purchase totals = $1,206.28       $1,319.7951   $1,319.79   $1,319.75   $1,319.90