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 $204.59   5.814%   $216.4849   $216.48   $216.50   $216.50  
  Purchase #2 $125.39   7.706%   $135.0526   $135.05   $135.05   $135.10  
  Purchase #3 $63.82   5.324%   $67.2178   $67.22   $67.20   $67.20  
  Purchase #4 $250.62   5.796%   $265.1459   $265.15   $265.15   $265.10  
  Purchase #5 $197.30   11.386%   $219.7646   $219.76   $219.75   $219.80  
  Purchase #6 $180.66   5.228%   $190.1049   $190.10   $190.10   $190.10  
  Purchase #7 $108.28   11.309%   $120.5254   $120.53   $120.55   $120.50  
  7 purchase totals = $1,130.66       $1,214.2961   $1,214.29   $1,214.30   $1,214.30