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 $223.98   13.561%   $254.3539   $254.35   $254.35   $254.40  
  Purchase #2 $211.89   6.771%   $226.2371   $226.24   $226.25   $226.20  
  Purchase #3 $8.92   7.421%   $9.582   $9.58   $9.60   $9.60  
  Purchase #4 $18.73   5.874%   $19.8302   $19.83   $19.85   $19.80  
  Purchase #5 $35.80   4.500%   $37.411   $37.41   $37.40   $37.40  
  Purchase #6 $68.94   8.314%   $74.6717   $74.67   $74.65   $74.70  
  Purchase #7 $131.79   13.267%   $149.2746   $149.27   $149.25   $149.30  
  7 purchase totals = $700.05       $771.3605   $771.35   $771.35   $771.40