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 $84.27   9.174%   $92.0009   $92.00   $92.00   $92.00  
  Purchase #2 $161.52   9.698%   $177.1842   $177.18   $177.20   $177.20  
  Purchase #3 $42.82   4.451%   $44.7259   $44.73   $44.75   $44.70  
  Purchase #4 $152.57   13.236%   $172.7642   $172.76   $172.75   $172.80  
  Purchase #5 $6.89   10.189%   $7.592   $7.59   $7.60   $7.60  
  Purchase #6 $167.63   13.299%   $189.9231   $189.92   $189.90   $189.90  
  Purchase #7 $118.31   5.277%   $124.5532   $124.55   $124.55   $124.60  
  7 purchase totals = $734.01       $808.7435   $808.73   $808.75   $808.80