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 $81.57   4.574%   $85.301   $85.30   $85.30   $85.30  
  Purchase #2 $239.76   8.822%   $260.9116   $260.91   $260.90   $260.90  
  Purchase #3 $145.39   10.860%   $161.1794   $161.18   $161.20   $161.20  
  Purchase #4 $62.93   3.665%   $65.2364   $65.24   $65.25   $65.20  
  Purchase #5 $187.81   9.479%   $205.6125   $205.61   $205.60   $205.60  
  Purchase #6 $68.45   9.781%   $75.1451   $75.15   $75.15   $75.10  
  Purchase #7 $108.28   3.645%   $112.2268   $112.23   $112.25   $112.20  
  7 purchase totals = $894.19       $965.6128   $965.62   $965.65   $965.50