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 $222.82   10.534%   $246.2919   $246.29   $246.30   $246.30  
  Purchase #2 $53.39   11.127%   $59.3307   $59.33   $59.35   $59.30  
  Purchase #3 $147.45   8.252%   $159.6176   $159.62   $159.60   $159.60  
  Purchase #4 $88.68   3.683%   $91.9461   $91.95   $91.95   $91.90  
  Purchase #5 $158.50   7.598%   $170.5428   $170.54   $170.55   $170.50  
  Purchase #6 $247.97   6.260%   $263.4929   $263.49   $263.50   $263.50  
  Purchase #7 $104.80   10.727%   $116.0419   $116.04   $116.05   $116.00  
  7 purchase totals = $1,023.61       $1,107.2639   $1,107.26   $1,107.30   $1,107.10