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 $29.37   13.517%   $33.3399   $33.34   $33.35   $33.30  
  Purchase #2 $158.97   10.623%   $175.8574   $175.86   $175.85   $175.90  
  Purchase #3 $242.69   13.116%   $274.5212   $274.52   $274.50   $274.50  
  Purchase #4 $133.31   10.236%   $146.9556   $146.96   $146.95   $147.00  
  Purchase #5 $92.71   12.629%   $104.4183   $104.42   $104.40   $104.40  
  Purchase #6 $160.52   3.495%   $166.1302   $166.13   $166.15   $166.10  
  Purchase #7 $85.69   10.244%   $94.4681   $94.47   $94.45   $94.50  
  7 purchase totals = $903.26       $995.6907   $995.70   $995.65   $995.70