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 $211.66   13.626%   $240.5008   $240.50   $240.50   $240.50  
  Purchase #2 $21.90   9.688%   $24.0217   $24.02   $24.00   $24.00  
  Purchase #3 $224.81   9.289%   $245.6926   $245.69   $245.70   $245.70  
  Purchase #4 $65.66   8.612%   $71.3146   $71.31   $71.30   $71.30  
  Purchase #5 $65.41   7.256%   $70.1561   $70.16   $70.15   $70.20  
  Purchase #6 $231.52   6.743%   $247.1314   $247.13   $247.15   $247.10  
  Purchase #7 $39.99   12.607%   $45.0315   $45.03   $45.05   $45.00  
  7 purchase totals = $860.95       $943.8487   $943.84   $943.85   $943.80