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 $151.36   3.139%   $156.1112   $156.11   $156.10   $156.10  
  Purchase #2 $88.76   12.327%   $99.7014   $99.70   $99.70   $99.70  
  Purchase #3 $77.39   13.295%   $87.679   $87.68   $87.70   $87.70  
  Purchase #4 $194.90   3.297%   $201.3259   $201.33   $201.35   $201.30  
  Purchase #5 $155.51   5.713%   $164.3943   $164.39   $164.40   $164.40  
  Purchase #6 $17.52   7.282%   $18.7958   $18.80   $18.80   $18.80  
  Purchase #7 $245.43   13.841%   $279.4   $279.40   $279.40   $279.40  
  7 purchase totals = $930.87       $1,007.4076   $1,007.41   $1,007.45   $1,007.40