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 $87.34   7.668%   $94.0372   $94.04   $94.05   $94.00  
  Purchase #2 $174.27   9.841%   $191.4199   $191.42   $191.40   $191.40  
  Purchase #3 $247.93   7.674%   $266.9561   $266.96   $266.95   $267.00  
  Purchase #4 $67.54   4.140%   $70.3362   $70.34   $70.35   $70.30  
  Purchase #5 $126.94   9.581%   $139.1021   $139.10   $139.10   $139.10  
  Purchase #6 $107.37   8.764%   $116.7799   $116.78   $116.80   $116.80  
  Purchase #7 $5.45   10.342%   $6.0136   $6.01   $6.00   $6.00  
  7 purchase totals = $816.84       $884.6450   $884.65   $884.65   $884.60