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 $32.50   3.444%   $33.6193   $33.62   $33.60   $33.60  
  Purchase #2 $34.63   5.857%   $36.6583   $36.66   $36.65   $36.70  
  Purchase #3 $233.86   12.284%   $262.5874   $262.59   $262.60   $262.60  
  Purchase #4 $98.97   3.658%   $102.5903   $102.59   $102.60   $102.60  
  Purchase #5 $59.63   11.762%   $66.6437   $66.64   $66.65   $66.60  
  Purchase #6 $89.35   6.254%   $94.9379   $94.94   $94.95   $94.90  
  Purchase #7 $190.96   11.350%   $212.634   $212.63   $212.65   $212.60  
  7 purchase totals = $739.90       $809.6709   $809.67   $809.70   $809.60