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 $141.99   7.856%   $153.1447   $153.14   $153.15   $153.10  
  Purchase #2 $92.82   3.865%   $96.4075   $96.41   $96.40   $96.40  
  Purchase #3 $8.56   11.283%   $9.5258   $9.53   $9.55   $9.50  
  Purchase #4 $177.44   10.379%   $195.8565   $195.86   $195.85   $195.90  
  Purchase #5 $220.54   6.614%   $235.1265   $235.13   $235.15   $235.10  
  Purchase #6 $41.52   13.552%   $47.1468   $47.15   $47.15   $47.10  
  Purchase #7 $57.52   12.545%   $64.7359   $64.74   $64.75   $64.70  
  7 purchase totals = $740.39       $801.9437   $801.96   $802.00   $801.80