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 $47.86   4.437%   $49.9835   $49.98   $50.00   $50.00  
  Purchase #2 $113.53   8.191%   $122.8292   $122.83   $122.85   $122.80  
  Purchase #3 $167.31   11.699%   $186.8836   $186.88   $186.90   $186.90  
  Purchase #4 $237.37   8.871%   $258.4271   $258.43   $258.45   $258.40  
  Purchase #5 $204.39   3.527%   $211.5988   $211.60   $211.60   $211.60  
  Purchase #6 $194.43   5.367%   $204.8651   $204.87   $204.85   $204.90  
  Purchase #7 $55.60   7.486%   $59.7622   $59.76   $59.75   $59.80  
  7 purchase totals = $1,020.49       $1,094.3495   $1,094.35   $1,094.40   $1,094.40