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 $187.57   5.220%   $197.3612   $197.36   $197.35   $197.40  
  Purchase #2 $95.58   9.515%   $104.6744   $104.67   $104.65   $104.70  
  Purchase #3 $120.36   4.284%   $125.5162   $125.52   $125.50   $125.50  
  Purchase #4 $59.97   5.255%   $63.1214   $63.12   $63.10   $63.10  
  Purchase #5 $114.80   10.223%   $126.536   $126.54   $126.55   $126.50  
  Purchase #6 $116.55   7.533%   $125.3297   $125.33   $125.35   $125.30  
  Purchase #7 $89.66   11.517%   $99.9861   $99.99   $100.00   $100.00  
  7 purchase totals = $784.49       $842.5250   $842.53   $842.50   $842.50