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 $180.86   12.536%   $203.5326   $203.53   $203.55   $203.50  
  Purchase #2 $131.86   9.629%   $144.5568   $144.56   $144.55   $144.60  
  Purchase #3 $205.41   8.429%   $222.724   $222.72   $222.70   $222.70  
  Purchase #4 $6.27   6.120%   $6.6537   $6.65   $6.65   $6.70  
  Purchase #5 $62.32   5.157%   $65.5338   $65.53   $65.55   $65.50  
  Purchase #6 $219.72   6.607%   $234.2369   $234.24   $234.25   $234.20  
  Purchase #7 $22.97   4.298%   $23.9573   $23.96   $23.95   $24.00  
  7 purchase totals = $829.41       $901.1951   $901.19   $901.20   $901.20