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 $62.52   9.660%   $68.5594   $68.56   $68.55   $68.60  
  Purchase #2 $170.56   6.221%   $181.1705   $181.17   $181.15   $181.20  
  Purchase #3 $233.92   11.258%   $260.2547   $260.25   $260.25   $260.30  
  Purchase #4 $49.49   9.194%   $54.0401   $54.04   $54.05   $54.00  
  Purchase #5 $6.44   13.817%   $7.3298   $7.33   $7.35   $7.30  
  Purchase #6 $51.59   4.584%   $53.9549   $53.95   $53.95   $54.00  
  Purchase #7 $215.43   4.863%   $225.9064   $225.91   $225.90   $225.90  
  7 purchase totals = $789.95       $851.2158   $851.21   $851.20   $851.30