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 $59.59   13.306%   $67.519   $67.52   $67.50   $67.50  
  Purchase #2 $242.47   6.113%   $257.2922   $257.29   $257.30   $257.30  
  Purchase #3 $177.72   6.226%   $188.7848   $188.78   $188.80   $188.80  
  Purchase #4 $122.30   3.195%   $126.2075   $126.21   $126.20   $126.20  
  Purchase #5 $85.34   4.295%   $89.0054   $89.01   $89.00   $89.00  
  Purchase #6 $232.28   12.157%   $260.5183   $260.52   $260.50   $260.50  
  Purchase #7 $14.97   5.424%   $15.782   $15.78   $15.80   $15.80  
  7 purchase totals = $934.67       $1,005.1092   $1,005.11   $1,005.10   $1,005.10