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 $84.78   9.694%   $92.9986   $93.00   $93.00   $93.00  
  Purchase #2 $165.92   5.252%   $174.6341   $174.63   $174.65   $174.60  
  Purchase #3 $27.27   7.184%   $29.2291   $29.23   $29.25   $29.20  
  Purchase #4 $107.38   7.207%   $115.1189   $115.12   $115.10   $115.10  
  Purchase #5 $33.26   9.416%   $36.3918   $36.39   $36.40   $36.40  
  Purchase #6 $153.38   8.580%   $166.54   $166.54   $166.55   $166.50  
  Purchase #7 $32.84   7.340%   $35.2505   $35.25   $35.25   $35.30  
  7 purchase totals = $604.83       $650.1630   $650.16   $650.20   $650.10