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 $204.60   6.559%   $218.0197   $218.02   $218.00   $218.00  
  Purchase #2 $197.26   3.228%   $203.6276   $203.63   $203.65   $203.60  
  Purchase #3 $174.65   3.585%   $180.9112   $180.91   $180.90   $180.90  
  Purchase #4 $199.79   5.259%   $210.297   $210.30   $210.30   $210.30  
  Purchase #5 $54.71   4.394%   $57.114   $57.11   $57.10   $57.10  
  Purchase #6 $215.67   6.854%   $230.452   $230.45   $230.45   $230.50  
  Purchase #7 $96.71   7.132%   $103.6074   $103.61   $103.60   $103.60  
  7 purchase totals = $1,143.39       $1,204.0289   $1,204.03   $1,204.00   $1,204.00