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 $46.94   8.532%   $50.9449   $50.94   $50.95   $50.90  
  Purchase #2 $194.92   11.214%   $216.7783   $216.78   $216.80   $216.80  
  Purchase #3 $248.73   6.699%   $265.3924   $265.39   $265.40   $265.40  
  Purchase #4 $120.53   12.669%   $135.7999   $135.80   $135.80   $135.80  
  Purchase #5 $142.68   12.613%   $160.6762   $160.68   $160.70   $160.70  
  Purchase #6 $107.33   12.219%   $120.4447   $120.44   $120.45   $120.40  
  Purchase #7 $172.36   6.609%   $183.7513   $183.75   $183.75   $183.80  
  7 purchase totals = $1,033.49       $1,133.7877   $1,133.78   $1,133.85   $1,133.80