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 $108.59   9.133%   $118.5075   $118.51   $118.50   $118.50  
  Purchase #2 $244.25   11.309%   $271.8722   $271.87   $271.85   $271.90  
  Purchase #3 $134.94   11.156%   $149.9939   $149.99   $150.00   $150.00  
  Purchase #4 $69.93   7.186%   $74.9552   $74.96   $74.95   $75.00  
  Purchase #5 $91.54   6.653%   $97.6302   $97.63   $97.65   $97.60  
  Purchase #6 $117.29   3.429%   $121.3119   $121.31   $121.30   $121.30  
  Purchase #7 $215.36   10.349%   $237.6476   $237.65   $237.65   $237.60  
  7 purchase totals = $981.90       $1,071.9185   $1,071.92   $1,071.90   $1,071.90