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 $114.87   5.447%   $121.127   $121.13   $121.15   $121.10  
  Purchase #2 $131.66   11.614%   $146.951   $146.95   $146.95   $147.00  
  Purchase #3 $193.91   11.535%   $216.2775   $216.28   $216.30   $216.30  
  Purchase #4 $25.76   12.187%   $28.8994   $28.90   $28.90   $28.90  
  Purchase #5 $192.77   7.722%   $207.6557   $207.66   $207.65   $207.70  
  Purchase #6 $208.93   3.741%   $216.7461   $216.75   $216.75   $216.70  
  Purchase #7 $50.35   11.218%   $55.9983   $56.00   $56.00   $56.00  
  7 purchase totals = $918.25       $993.6550   $993.67   $993.70   $993.70