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 $236.55   11.514%   $263.7864   $263.79   $263.80   $263.80  
  Purchase #2 $109.63   6.112%   $116.3306   $116.33   $116.35   $116.30  
  Purchase #3 $69.94   8.256%   $75.7142   $75.71   $75.70   $75.70  
  Purchase #4 $91.33   12.199%   $102.4713   $102.47   $102.45   $102.50  
  Purchase #5 $23.26   8.610%   $25.2627   $25.26   $25.25   $25.30  
  Purchase #6 $184.84   10.121%   $203.5477   $203.55   $203.55   $203.50  
  Purchase #7 $142.55   3.749%   $147.8942   $147.89   $147.90   $147.90  
  7 purchase totals = $858.10       $935.0071   $935.00   $935.00   $935.00