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 $218.40   6.771%   $233.1879   $233.19   $233.20   $233.20  
  Purchase #2 $156.92   11.238%   $174.5547   $174.55   $174.55   $174.60  
  Purchase #3 $173.42   6.619%   $184.8987   $184.90   $184.90   $184.90  
  Purchase #4 $245.35   8.566%   $266.3667   $266.37   $266.35   $266.40  
  Purchase #5 $168.30   12.317%   $189.0295   $189.03   $189.05   $189.00  
  Purchase #6 $42.64   4.471%   $44.5464   $44.55   $44.55   $44.50  
  Purchase #7 $228.99   6.737%   $244.4171   $244.42   $244.40   $244.40  
  7 purchase totals = $1,234.02       $1,337.0010   $1,337.01   $1,337.00   $1,337.00