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 $141.67   4.283%   $147.7377   $147.74   $147.75   $147.70  
  Purchase #2 $212.74   3.389%   $219.9498   $219.95   $219.95   $219.90  
  Purchase #3 $87.92   7.132%   $94.1905   $94.19   $94.20   $94.20  
  Purchase #4 $58.75   7.578%   $63.2021   $63.20   $63.20   $63.20  
  Purchase #5 $178.71   11.186%   $198.7005   $198.70   $198.70   $198.70  
  Purchase #6 $20.37   8.673%   $22.1367   $22.14   $22.15   $22.10  
  Purchase #7 $19.68   11.301%   $21.904   $21.90   $21.90   $21.90  
  7 purchase totals = $719.84       $767.8213   $767.82   $767.85   $767.70