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 $52.83   3.164%   $54.5015   $54.50   $54.50   $54.50  
  Purchase #2 $124.67   6.405%   $132.6551   $132.66   $132.65   $132.70  
  Purchase #3 $137.92   11.206%   $153.3753   $153.38   $153.40   $153.40  
  Purchase #4 $88.41   8.573%   $95.9894   $95.99   $96.00   $96.00  
  Purchase #5 $5.45   5.355%   $5.7418   $5.74   $5.75   $5.70  
  Purchase #6 $70.59   11.437%   $78.6634   $78.66   $78.65   $78.70  
  Purchase #7 $250.56   6.339%   $266.443   $266.44   $266.45   $266.40  
  7 purchase totals = $730.43       $787.3695   $787.37   $787.40   $787.40