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 $223.51   13.769%   $254.2851   $254.29   $254.30   $254.30  
  Purchase #2 $107.62   11.171%   $119.6422   $119.64   $119.65   $119.60  
  Purchase #3 $38.69   11.784%   $43.2492   $43.25   $43.25   $43.20  
  Purchase #4 $65.70   9.630%   $72.0269   $72.03   $72.05   $72.00  
  Purchase #5 $12.81   11.790%   $14.3203   $14.32   $14.30   $14.30  
  Purchase #6 $66.97   8.102%   $72.3959   $72.40   $72.40   $72.40  
  Purchase #7 $186.96   9.754%   $205.1961   $205.20   $205.20   $205.20  
  7 purchase totals = $702.26       $781.1157   $781.13   $781.15   $781.00