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 $76.60   8.368%   $83.0099   $83.01   $83.00   $83.00  
  Purchase #2 $232.39   5.437%   $245.025   $245.03   $245.05   $245.00  
  Purchase #3 $175.93   6.444%   $187.2669   $187.27   $187.25   $187.30  
  Purchase #4 $221.46   11.104%   $246.0509   $246.05   $246.05   $246.10  
  Purchase #5 $101.70   8.540%   $110.3852   $110.39   $110.40   $110.40  
  Purchase #6 $232.66   11.731%   $259.9533   $259.95   $259.95   $260.00  
  Purchase #7 $109.53   9.360%   $119.782   $119.78   $119.80   $119.80  
  7 purchase totals = $1,150.27       $1,251.4732   $1,251.48   $1,251.50   $1,251.60