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 $159.44   4.586%   $166.7519   $166.75   $166.75   $166.80  
  Purchase #2 $188.92   7.454%   $203.0021   $203.00   $203.00   $203.00  
  Purchase #3 $59.30   6.813%   $63.3401   $63.34   $63.35   $63.30  
  Purchase #4 $73.87   3.165%   $76.208   $76.21   $76.20   $76.20  
  Purchase #5 $126.25   4.174%   $131.5197   $131.52   $131.50   $131.50  
  Purchase #6 $96.26   9.452%   $105.3585   $105.36   $105.35   $105.40  
  Purchase #7 $10.67   12.719%   $12.0271   $12.03   $12.05   $12.00  
  7 purchase totals = $714.71       $758.2074   $758.21   $758.20   $758.20