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 $246.73   5.512%   $260.3298   $260.33   $260.35   $260.30  
  Purchase #2 $240.72   8.424%   $260.9983   $261.00   $261.00   $261.00  
  Purchase #3 $23.98   9.391%   $26.232   $26.23   $26.25   $26.20  
  Purchase #4 $149.84   6.372%   $159.3878   $159.39   $159.40   $159.40  
  Purchase #5 $182.90   10.843%   $202.7318   $202.73   $202.75   $202.70  
  Purchase #6 $142.35   10.434%   $157.2028   $157.20   $157.20   $157.20  
  Purchase #7 $194.89   3.764%   $202.2257   $202.23   $202.25   $202.20  
  7 purchase totals = $1,181.41       $1,269.1082   $1,269.11   $1,269.20   $1,269.00