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 $54.46   8.361%   $59.0134   $59.01   $59.00   $59.00  
  Purchase #2 $234.87   6.154%   $249.3239   $249.32   $249.30   $249.30  
  Purchase #3 $218.25   5.553%   $230.3694   $230.37   $230.35   $230.40  
  Purchase #4 $229.28   4.275%   $239.0817   $239.08   $239.10   $239.10  
  Purchase #5 $46.68   5.410%   $49.2054   $49.21   $49.20   $49.20  
  Purchase #6 $140.39   3.447%   $145.2292   $145.23   $145.25   $145.20  
  Purchase #7 $189.44   12.478%   $213.0783   $213.08   $213.10   $213.10  
  7 purchase totals = $1,113.37       $1,185.3013   $1,185.30   $1,185.30   $1,185.30