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 $232.44   10.330%   $256.4511   $256.45   $256.45   $256.50  
  Purchase #2 $49.97   8.754%   $54.3444   $54.34   $54.35   $54.30  
  Purchase #3 $120.58   9.575%   $132.1255   $132.13   $132.15   $132.10  
  Purchase #4 $70.50   8.591%   $76.5567   $76.56   $76.55   $76.60  
  Purchase #5 $72.85   8.598%   $79.1136   $79.11   $79.10   $79.10  
  Purchase #6 $248.50   13.456%   $281.9382   $281.94   $281.95   $281.90  
  Purchase #7 $139.71   10.759%   $154.7414   $154.74   $154.75   $154.70  
  7 purchase totals = $934.55       $1,035.2709   $1,035.27   $1,035.30   $1,035.20