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 $83.87   12.488%   $94.3437   $94.34   $94.35   $94.30  
  Purchase #2 $69.45   7.503%   $74.6608   $74.66   $74.65   $74.70  
  Purchase #3 $52.46   8.813%   $57.0833   $57.08   $57.10   $57.10  
  Purchase #4 $89.89   5.240%   $94.6002   $94.60   $94.60   $94.60  
  Purchase #5 $71.80   7.139%   $76.9258   $76.93   $76.95   $76.90  
  Purchase #6 $133.49   7.272%   $143.1974   $143.20   $143.20   $143.20  
  Purchase #7 $202.67   8.708%   $220.3185   $220.32   $220.30   $220.30  
  7 purchase totals = $703.63       $761.1297   $761.13   $761.15   $761.10