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 $82.65   12.519%   $92.997   $93.00   $93.00   $93.00  
  Purchase #2 $156.29   11.689%   $174.5587   $174.56   $174.55   $174.60  
  Purchase #3 $77.46   12.843%   $87.4082   $87.41   $87.40   $87.40  
  Purchase #4 $89.38   8.108%   $96.6269   $96.63   $96.65   $96.60  
  Purchase #5 $105.96   10.362%   $116.9396   $116.94   $116.95   $116.90  
  Purchase #6 $16.25   12.321%   $18.2522   $18.25   $18.25   $18.30  
  Purchase #7 $213.89   11.743%   $239.0071   $239.01   $239.00   $239.00  
  7 purchase totals = $741.88       $825.7897   $825.80   $825.80   $825.80