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 $242.77   9.412%   $265.6195   $265.62   $265.60   $265.60  
  Purchase #2 $216.94   12.171%   $243.3438   $243.34   $243.35   $243.30  
  Purchase #3 $123.72   12.221%   $138.8398   $138.84   $138.85   $138.80  
  Purchase #4 $46.53   4.326%   $48.5429   $48.54   $48.55   $48.50  
  Purchase #5 $150.50   13.205%   $170.3735   $170.37   $170.35   $170.40  
  Purchase #6 $177.80   9.561%   $194.7995   $194.80   $194.80   $194.80  
  Purchase #7 $108.34   6.521%   $115.4049   $115.40   $115.40   $115.40  
  7 purchase totals = $1,066.60       $1,176.9239   $1,176.91   $1,176.90   $1,176.80