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 $57.52   13.801%   $65.4583   $65.46   $65.45   $65.50  
  Purchase #2 $120.74   5.655%   $127.5678   $127.57   $127.55   $127.60  
  Purchase #3 $46.32   9.471%   $50.707   $50.71   $50.70   $50.70  
  Purchase #4 $112.45   6.264%   $119.4939   $119.49   $119.50   $119.50  
  Purchase #5 $246.73   6.487%   $262.7354   $262.74   $262.75   $262.70  
  Purchase #6 $5.35   12.477%   $6.0175   $6.02   $6.00   $6.00  
  Purchase #7 $111.87   8.474%   $121.3499   $121.35   $121.35   $121.30  
  7 purchase totals = $700.98       $753.3298   $753.34   $753.30   $753.30