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 $197.57   5.282%   $208.0056   $208.01   $208.00   $208.00  
  Purchase #2 $145.80   11.281%   $162.2477   $162.25   $162.25   $162.20  
  Purchase #3 $235.44   4.652%   $246.3927   $246.39   $246.40   $246.40  
  Purchase #4 $249.88   7.289%   $268.0938   $268.09   $268.10   $268.10  
  Purchase #5 $244.52   12.582%   $275.2855   $275.29   $275.30   $275.30  
  Purchase #6 $95.67   3.441%   $98.962   $98.96   $98.95   $99.00  
  Purchase #7 $136.89   9.330%   $149.6618   $149.66   $149.65   $149.70  
  7 purchase totals = $1,305.77       $1,408.6491   $1,408.65   $1,408.65   $1,408.70