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 $48.64   10.512%   $53.753   $53.75   $53.75   $53.80  
  Purchase #2 $109.60   8.361%   $118.7637   $118.76   $118.75   $118.80  
  Purchase #3 $111.44   7.171%   $119.4314   $119.43   $119.45   $119.40  
  Purchase #4 $162.66   9.724%   $178.4771   $178.48   $178.50   $178.50  
  Purchase #5 $93.94   13.430%   $106.5561   $106.56   $106.55   $106.60  
  Purchase #6 $165.67   3.246%   $171.0476   $171.05   $171.05   $171.00  
  Purchase #7 $119.82   3.629%   $124.1683   $124.17   $124.15   $124.20  
  7 purchase totals = $811.77       $872.1972   $872.20   $872.20   $872.30