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 $245.90   8.386%   $266.5212   $266.52   $266.50   $266.50  
  Purchase #2 $188.73   7.376%   $202.6507   $202.65   $202.65   $202.70  
  Purchase #3 $25.51   5.333%   $26.8704   $26.87   $26.85   $26.90  
  Purchase #4 $173.71   6.163%   $184.4157   $184.42   $184.40   $184.40  
  Purchase #5 $209.25   6.846%   $223.5753   $223.58   $223.60   $223.60  
  Purchase #6 $228.39   11.739%   $255.2007   $255.20   $255.20   $255.20  
  Purchase #7 $76.26   12.172%   $85.5424   $85.54   $85.55   $85.50  
  7 purchase totals = $1,147.75       $1,244.7764   $1,244.78   $1,244.75   $1,244.80