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 $205.46   3.681%   $213.023   $213.02   $213.00   $213.00  
  Purchase #2 $210.72   6.359%   $224.1197   $224.12   $224.10   $224.10  
  Purchase #3 $139.42   9.190%   $152.2327   $152.23   $152.25   $152.20  
  Purchase #4 $96.94   13.270%   $109.8039   $109.80   $109.80   $109.80  
  Purchase #5 $23.94   10.552%   $26.4661   $26.47   $26.45   $26.50  
  Purchase #6 $159.55   5.198%   $167.8434   $167.84   $167.85   $167.80  
  Purchase #7 $107.73   8.556%   $116.9474   $116.95   $116.95   $116.90  
  7 purchase totals = $943.76       $1,010.4362   $1,010.43   $1,010.40   $1,010.30