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 $203.46   5.682%   $215.0206   $215.02   $215.00   $215.00  
  Purchase #2 $149.65   12.283%   $168.0315   $168.03   $168.05   $168.00  
  Purchase #3 $6.73   8.530%   $7.3041   $7.30   $7.30   $7.30  
  Purchase #4 $220.31   12.356%   $247.5315   $247.53   $247.55   $247.50  
  Purchase #5 $49.81   11.557%   $55.5665   $55.57   $55.55   $55.60  
  Purchase #6 $122.47   3.167%   $126.3486   $126.35   $126.35   $126.30  
  Purchase #7 $12.68   9.715%   $13.9119   $13.91   $13.90   $13.90  
  7 purchase totals = $765.11       $833.7147   $833.71   $833.70   $833.60