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 $62.33   13.591%   $70.8013   $70.80   $70.80   $70.80  
  Purchase #2 $210.82   6.750%   $225.0504   $225.05   $225.05   $225.10  
  Purchase #3 $165.53   6.150%   $175.7101   $175.71   $175.70   $175.70  
  Purchase #4 $122.29   9.299%   $133.6617   $133.66   $133.65   $133.70  
  Purchase #5 $35.95   9.346%   $39.3099   $39.31   $39.30   $39.30  
  Purchase #6 $208.78   8.262%   $226.0294   $226.03   $226.05   $226.00  
  Purchase #7 $62.54   6.512%   $66.6126   $66.61   $66.60   $66.60  
  7 purchase totals = $868.24       $937.1754   $937.17   $937.15   $937.20