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 $119.65   11.181%   $133.0281   $133.03   $133.05   $133.00  
  Purchase #2 $157.39   9.279%   $171.9942   $171.99   $172.00   $172.00  
  Purchase #3 $61.91   6.508%   $65.9391   $65.94   $65.95   $65.90  
  Purchase #4 $124.56   9.180%   $135.9946   $135.99   $136.00   $136.00  
  Purchase #5 $53.92   10.391%   $59.5228   $59.52   $59.50   $59.50  
  Purchase #6 $242.35   6.506%   $258.1173   $258.12   $258.10   $258.10  
  Purchase #7 $40.56   10.614%   $44.865   $44.87   $44.85   $44.90  
  7 purchase totals = $800.34       $869.4611   $869.46   $869.45   $869.40