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 $60.79   7.452%   $65.3201   $65.32   $65.30   $65.30  
  Purchase #2 $236.88   8.339%   $256.6334   $256.63   $256.65   $256.60  
  Purchase #3 $205.79   10.257%   $226.8979   $226.90   $226.90   $226.90  
  Purchase #4 $210.53   9.821%   $231.2062   $231.21   $231.20   $231.20  
  Purchase #5 $236.73   7.657%   $254.8564   $254.86   $254.85   $254.90  
  Purchase #6 $116.81   7.311%   $125.35   $125.35   $125.35   $125.40  
  Purchase #7 $91.77   13.217%   $103.8992   $103.90   $103.90   $103.90  
  7 purchase totals = $1,159.30       $1,264.1632   $1,264.17   $1,264.15   $1,264.20