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 $130.68   5.102%   $137.3473   $137.35   $137.35   $137.30  
  Purchase #2 $153.36   11.213%   $170.5563   $170.56   $170.55   $170.60  
  Purchase #3 $240.53   11.465%   $268.1068   $268.11   $268.10   $268.10  
  Purchase #4 $118.31   13.792%   $134.6273   $134.63   $134.65   $134.60  
  Purchase #5 $211.52   3.257%   $218.4092   $218.41   $218.40   $218.40  
  Purchase #6 $150.73   3.131%   $155.4494   $155.45   $155.45   $155.40  
  Purchase #7 $206.29   6.142%   $218.9603   $218.96   $218.95   $219.00  
  7 purchase totals = $1,211.42       $1,303.4566   $1,303.47   $1,303.45   $1,303.40