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 $175.61   8.174%   $189.9644   $189.96   $189.95   $190.00  
  Purchase #2 $237.77   4.265%   $247.9109   $247.91   $247.90   $247.90  
  Purchase #3 $244.67   3.134%   $252.338   $252.34   $252.35   $252.30  
  Purchase #4 $53.76   13.237%   $60.8762   $60.88   $60.90   $60.90  
  Purchase #5 $62.64   12.453%   $70.4406   $70.44   $70.45   $70.40  
  Purchase #6 $161.86   3.782%   $167.9815   $167.98   $168.00   $168.00  
  Purchase #7 $187.26   13.607%   $212.7405   $212.74   $212.75   $212.70  
  7 purchase totals = $1,123.57       $1,202.2521   $1,202.25   $1,202.30   $1,202.20