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 $54.29   10.478%   $59.9785   $59.98   $60.00   $60.00  
  Purchase #2 $107.71   13.319%   $122.0559   $122.06   $122.05   $122.10  
  Purchase #3 $147.48   9.805%   $161.9404   $161.94   $161.95   $161.90  
  Purchase #4 $182.67   10.477%   $201.8083   $201.81   $201.80   $201.80  
  Purchase #5 $86.88   12.767%   $97.972   $97.97   $97.95   $98.00  
  Purchase #6 $123.26   13.366%   $139.7349   $139.73   $139.75   $139.70  
  Purchase #7 $41.62   12.206%   $46.7001   $46.70   $46.70   $46.70  
  7 purchase totals = $743.91       $830.1901   $830.19   $830.20   $830.20