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 $80.38   5.426%   $84.7414   $84.74   $84.75   $84.70  
  Purchase #2 $58.34   13.131%   $66.0006   $66.00   $66.00   $66.00  
  Purchase #3 $114.90   8.373%   $124.5206   $124.52   $124.50   $124.50  
  Purchase #4 $192.72   9.452%   $210.9359   $210.94   $210.95   $210.90  
  Purchase #5 $30.30   4.794%   $31.7526   $31.75   $31.75   $31.80  
  Purchase #6 $49.90   5.535%   $52.662   $52.66   $52.65   $52.70  
  Purchase #7 $163.85   11.324%   $182.4044   $182.40   $182.40   $182.40  
  7 purchase totals = $690.39       $753.0175   $753.01   $753.00   $753.00