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 $232.87   12.601%   $262.2139   $262.21   $262.20   $262.20  
  Purchase #2 $211.31   3.638%   $218.9975   $219.00   $219.00   $219.00  
  Purchase #3 $87.59   8.284%   $94.846   $94.85   $94.85   $94.80  
  Purchase #4 $61.35   3.548%   $63.5267   $63.53   $63.55   $63.50  
  Purchase #5 $60.47   10.589%   $66.8732   $66.87   $66.85   $66.90  
  Purchase #6 $158.96   3.468%   $164.4727   $164.47   $164.45   $164.50  
  Purchase #7 $229.41   7.264%   $246.0743   $246.07   $246.05   $246.10  
  7 purchase totals = $1,041.96       $1,117.0043   $1,117.00   $1,116.95   $1,117.00