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 $236.50   12.147%   $265.2277   $265.23   $265.25   $265.20  
  Purchase #2 $178.91   8.600%   $194.2963   $194.30   $194.30   $194.30  
  Purchase #3 $27.66   5.713%   $29.2402   $29.24   $29.25   $29.20  
  Purchase #4 $193.82   5.610%   $204.6933   $204.69   $204.70   $204.70  
  Purchase #5 $174.52   7.633%   $187.8411   $187.84   $187.85   $187.80  
  Purchase #6 $10.25   8.365%   $11.1074   $11.11   $11.10   $11.10  
  Purchase #7 $225.72   8.167%   $244.1546   $244.15   $244.15   $244.20  
  7 purchase totals = $1,047.38       $1,136.5606   $1,136.56   $1,136.60   $1,136.50