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 $179.25   13.252%   $203.0042   $203.00   $203.00   $203.00  
  Purchase #2 $191.99   12.327%   $215.6566   $215.66   $215.65   $215.70  
  Purchase #3 $155.42   12.599%   $175.0014   $175.00   $175.00   $175.00  
  Purchase #4 $50.31   6.562%   $53.6113   $53.61   $53.60   $53.60  
  Purchase #5 $26.57   7.492%   $28.5606   $28.56   $28.55   $28.60  
  Purchase #6 $102.52   12.167%   $114.9936   $114.99   $115.00   $115.00  
  Purchase #7 $50.99   7.360%   $54.7429   $54.74   $54.75   $54.70  
  7 purchase totals = $757.05       $845.5706   $845.56   $845.55   $845.60