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 $218.76   8.172%   $236.6371   $236.64   $236.65   $236.60  
  Purchase #2 $200.85   9.684%   $220.3003   $220.30   $220.30   $220.30  
  Purchase #3 $94.87   7.678%   $102.1541   $102.15   $102.15   $102.20  
  Purchase #4 $25.81   5.485%   $27.2257   $27.23   $27.25   $27.20  
  Purchase #5 $143.69   4.184%   $149.702   $149.70   $149.70   $149.70  
  Purchase #6 $56.51   13.214%   $63.9772   $63.98   $64.00   $64.00  
  Purchase #7 $209.51   11.539%   $233.6854   $233.69   $233.70   $233.70  
  7 purchase totals = $950.00       $1,033.6818   $1,033.69   $1,033.75   $1,033.70