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 $228.97   3.510%   $237.0068   $237.01   $237.00   $237.00  
  Purchase #2 $127.80   6.314%   $135.8693   $135.87   $135.85   $135.90  
  Purchase #3 $181.27   5.763%   $191.7166   $191.72   $191.70   $191.70  
  Purchase #4 $240.66   9.125%   $262.6202   $262.62   $262.60   $262.60  
  Purchase #5 $126.31   11.216%   $140.4769   $140.48   $140.50   $140.50  
  Purchase #6 $161.52   5.307%   $170.0919   $170.09   $170.10   $170.10  
  Purchase #7 $90.86   6.193%   $96.487   $96.49   $96.50   $96.50  
  7 purchase totals = $1,157.39       $1,234.2687   $1,234.28   $1,234.25   $1,234.30