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 $241.78   12.746%   $272.5973   $272.60   $272.60   $272.60  
  Purchase #2 $131.97   3.183%   $136.1706   $136.17   $136.15   $136.20  
  Purchase #3 $39.86   8.475%   $43.2381   $43.24   $43.25   $43.20  
  Purchase #4 $137.78   8.421%   $149.3825   $149.38   $149.40   $149.40  
  Purchase #5 $171.38   13.647%   $194.7682   $194.77   $194.75   $194.80  
  Purchase #6 $204.48   3.684%   $212.013   $212.01   $212.00   $212.00  
  Purchase #7 $225.88   5.649%   $238.64   $238.64   $238.65   $238.60  
  7 purchase totals = $1,153.13       $1,246.8097   $1,246.81   $1,246.80   $1,246.80