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 $188.87   7.822%   $203.6434   $203.64   $203.65   $203.60  
  Purchase #2 $35.91   3.769%   $37.2634   $37.26   $37.25   $37.30  
  Purchase #3 $35.55   7.718%   $38.2937   $38.29   $38.30   $38.30  
  Purchase #4 $235.86   5.679%   $249.2545   $249.25   $249.25   $249.30  
  Purchase #5 $6.36   9.185%   $6.9442   $6.94   $6.95   $6.90  
  Purchase #6 $119.51   10.311%   $131.8327   $131.83   $131.85   $131.80  
  Purchase #7 $81.52   6.449%   $86.7772   $86.78   $86.80   $86.80  
  7 purchase totals = $703.58       $754.0091   $753.99   $754.05   $754.00