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 $61.41   10.861%   $68.0797   $68.08   $68.10   $68.10  
  Purchase #2 $62.97   6.396%   $66.9976   $67.00   $67.00   $67.00  
  Purchase #3 $16.59   9.387%   $18.1473   $18.15   $18.15   $18.10  
  Purchase #4 $145.55   8.562%   $158.012   $158.01   $158.00   $158.00  
  Purchase #5 $156.85   4.795%   $164.371   $164.37   $164.35   $164.40  
  Purchase #6 $9.37   6.644%   $9.9925   $9.99   $10.00   $10.00  
  Purchase #7 $115.35   3.537%   $119.4299   $119.43   $119.45   $119.40  
  7 purchase totals = $568.09       $605.0300   $605.03   $605.05   $605.00