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 $58.78   13.561%   $66.7512   $66.75   $66.75   $66.80  
  Purchase #2 $171.56   7.845%   $185.0189   $185.02   $185.00   $185.00  
  Purchase #3 $23.59   10.390%   $26.041   $26.04   $26.05   $26.00  
  Purchase #4 $75.30   5.347%   $79.3263   $79.33   $79.35   $79.30  
  Purchase #5 $90.26   8.484%   $97.9177   $97.92   $97.90   $97.90  
  Purchase #6 $16.50   3.263%   $17.0384   $17.04   $17.05   $17.00  
  Purchase #7 $219.89   7.326%   $235.9991   $236.00   $236.00   $236.00  
  7 purchase totals = $655.88       $708.0926   $708.10   $708.10   $708.00