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 $82.73   12.323%   $92.9248   $92.92   $92.90   $92.90  
  Purchase #2 $65.27   3.683%   $67.6739   $67.67   $67.65   $67.70  
  Purchase #3 $53.82   9.112%   $58.7241   $58.72   $58.70   $58.70  
  Purchase #4 $230.31   3.866%   $239.2138   $239.21   $239.20   $239.20  
  Purchase #5 $75.51   12.572%   $85.0031   $85.00   $85.00   $85.00  
  Purchase #6 $121.46   5.364%   $127.9751   $127.98   $128.00   $128.00  
  Purchase #7 $214.49   13.459%   $243.3582   $243.36   $243.35   $243.40  
  7 purchase totals = $843.59       $914.8730   $914.86   $914.80   $914.90