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 $233.69   10.834%   $259.008   $259.01   $259.00   $259.00  
  Purchase #2 $21.58   4.426%   $22.5351   $22.54   $22.55   $22.50  
  Purchase #3 $47.98   6.315%   $51.0099   $51.01   $51.00   $51.00  
  Purchase #4 $180.62   3.144%   $186.2987   $186.30   $186.30   $186.30  
  Purchase #5 $154.53   12.125%   $173.2668   $173.27   $173.25   $173.30  
  Purchase #6 $56.97   12.669%   $64.1875   $64.19   $64.20   $64.20  
  Purchase #7 $233.83   13.125%   $264.5202   $264.52   $264.50   $264.50  
  7 purchase totals = $929.20       $1,020.8262   $1,020.84   $1,020.80   $1,020.80