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 $46.89   4.854%   $49.166   $49.17   $49.15   $49.20  
  Purchase #2 $195.93   7.765%   $211.144   $211.14   $211.15   $211.10  
  Purchase #3 $44.84   3.803%   $46.5453   $46.55   $46.55   $46.50  
  Purchase #4 $16.74   7.413%   $17.9809   $17.98   $18.00   $18.00  
  Purchase #5 $173.65   5.477%   $183.1608   $183.16   $183.15   $183.20  
  Purchase #6 $39.45   5.457%   $41.6028   $41.60   $41.60   $41.60  
  Purchase #7 $186.88   12.190%   $209.6607   $209.66   $209.65   $209.70  
  7 purchase totals = $704.38       $759.2605   $759.26   $759.25   $759.30