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 $11.63   6.855%   $12.4272   $12.43   $12.45   $12.40  
  Purchase #2 $217.66   13.220%   $246.4347   $246.43   $246.45   $246.40  
  Purchase #3 $169.66   11.373%   $188.9554   $188.96   $188.95   $189.00  
  Purchase #4 $186.51   5.428%   $196.6338   $196.63   $196.65   $196.60  
  Purchase #5 $183.61   6.143%   $194.8892   $194.89   $194.90   $194.90  
  Purchase #6 $250.70   5.737%   $265.0827   $265.08   $265.10   $265.10  
  Purchase #7 $247.65   7.873%   $267.1475   $267.15   $267.15   $267.10  
  7 purchase totals = $1,267.42       $1,371.5705   $1,371.57   $1,371.65   $1,371.50