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 $218.48   8.459%   $236.9612   $236.96   $236.95   $237.00  
  Purchase #2 $160.61   10.787%   $177.935   $177.94   $177.95   $177.90  
  Purchase #3 $57.37   4.106%   $59.7256   $59.73   $59.75   $59.70  
  Purchase #4 $225.27   9.731%   $247.191   $247.19   $247.20   $247.20  
  Purchase #5 $11.85   7.483%   $12.7367   $12.74   $12.75   $12.70  
  Purchase #6 $6.83   3.139%   $7.0444   $7.04   $7.05   $7.00  
  Purchase #7 $139.31   4.218%   $145.1861   $145.19   $145.20   $145.20  
  7 purchase totals = $819.72       $886.7800   $886.79   $886.85   $886.70