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 $215.82   10.152%   $237.73   $237.73   $237.75   $237.70  
  Purchase #2 $203.42   11.433%   $226.677   $226.68   $226.70   $226.70  
  Purchase #3 $151.31   4.395%   $157.9601   $157.96   $157.95   $158.00  
  Purchase #4 $96.61   13.510%   $109.662   $109.66   $109.65   $109.70  
  Purchase #5 $49.36   10.805%   $54.6933   $54.69   $54.70   $54.70  
  Purchase #6 $151.25   11.741%   $169.0083   $169.01   $169.00   $169.00  
  Purchase #7 $126.78   7.394%   $136.1541   $136.15   $136.15   $136.20  
  7 purchase totals = $994.55       $1,091.8848   $1,091.88   $1,091.90   $1,092.00