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 $71.65   12.836%   $80.847   $80.85   $80.85   $80.80  
  Purchase #2 $89.39   6.865%   $95.5266   $95.53   $95.55   $95.50  
  Purchase #3 $54.57   11.727%   $60.9694   $60.97   $60.95   $61.00  
  Purchase #4 $48.88   8.227%   $52.9014   $52.90   $52.90   $52.90  
  Purchase #5 $161.35   12.457%   $181.4494   $181.45   $181.45   $181.40  
  Purchase #6 $211.96   10.731%   $234.7054   $234.71   $234.70   $234.70  
  Purchase #7 $223.87   9.512%   $245.1645   $245.16   $245.15   $245.20  
  7 purchase totals = $861.67       $951.5637   $951.57   $951.55   $951.50