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 $93.62   3.667%   $97.053   $97.05   $97.05   $97.10  
  Purchase #2 $38.92   6.646%   $41.5066   $41.51   $41.50   $41.50  
  Purchase #3 $233.93   4.463%   $244.3703   $244.37   $244.35   $244.40  
  Purchase #4 $211.91   12.162%   $237.6825   $237.68   $237.70   $237.70  
  Purchase #5 $241.86   6.312%   $257.1262   $257.13   $257.15   $257.10  
  Purchase #6 $24.38   5.761%   $25.7845   $25.78   $25.80   $25.80  
  Purchase #7 $134.47   8.305%   $145.6377   $145.64   $145.65   $145.60  
  7 purchase totals = $979.09       $1,049.1608   $1,049.16   $1,049.20   $1,049.20