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 $217.84   12.621%   $245.3336   $245.33   $245.35   $245.30  
  Purchase #2 $208.54   4.303%   $217.5135   $217.51   $217.50   $217.50  
  Purchase #3 $13.57   3.465%   $14.0402   $14.04   $14.05   $14.00  
  Purchase #4 $153.67   12.163%   $172.3609   $172.36   $172.35   $172.40  
  Purchase #5 $142.96   7.730%   $154.0108   $154.01   $154.00   $154.00  
  Purchase #6 $201.29   5.781%   $212.9266   $212.93   $212.95   $212.90  
  Purchase #7 $218.84   7.238%   $234.6796   $234.68   $234.70   $234.70  
  7 purchase totals = $1,156.71       $1,250.8652   $1,250.86   $1,250.90   $1,250.80