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 $233.86   5.679%   $247.1409   $247.14   $247.15   $247.10  
  Purchase #2 $236.26   8.370%   $256.035   $256.04   $256.05   $256.00  
  Purchase #3 $24.31   13.176%   $27.5131   $27.51   $27.50   $27.50  
  Purchase #4 $58.66   6.235%   $62.3175   $62.32   $62.30   $62.30  
  Purchase #5 $232.44   5.357%   $244.8918   $244.89   $244.90   $244.90  
  Purchase #6 $211.29   11.685%   $235.9792   $235.98   $236.00   $236.00  
  Purchase #7 $141.72   13.266%   $160.5206   $160.52   $160.50   $160.50  
  7 purchase totals = $1,138.54       $1,234.3981   $1,234.40   $1,234.40   $1,234.30