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 $195.59   12.866%   $220.7546   $220.75   $220.75   $220.80  
  Purchase #2 $219.61   9.550%   $240.5828   $240.58   $240.60   $240.60  
  Purchase #3 $161.73   3.496%   $167.3841   $167.38   $167.40   $167.40  
  Purchase #4 $133.94   8.552%   $145.3945   $145.39   $145.40   $145.40  
  Purchase #5 $197.61   5.193%   $207.8719   $207.87   $207.85   $207.90  
  Purchase #6 $156.84   6.854%   $167.5898   $167.59   $167.60   $167.60  
  Purchase #7 $234.68   7.823%   $253.039   $253.04   $253.05   $253.00  
  7 purchase totals = $1,300.00       $1,402.6167   $1,402.60   $1,402.65   $1,402.70