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 $229.74   13.396%   $260.516   $260.52   $260.50   $260.50  
  Purchase #2 $145.64   11.676%   $162.6449   $162.64   $162.65   $162.60  
  Purchase #3 $195.31   4.779%   $204.6439   $204.64   $204.65   $204.60  
  Purchase #4 $239.35   4.661%   $250.5061   $250.51   $250.50   $250.50  
  Purchase #5 $93.74   5.198%   $98.6126   $98.61   $98.60   $98.60  
  Purchase #6 $205.33   12.271%   $230.526   $230.53   $230.55   $230.50  
  Purchase #7 $160.95   5.173%   $169.2759   $169.28   $169.30   $169.30  
  7 purchase totals = $1,270.06       $1,376.7254   $1,376.73   $1,376.75   $1,376.60