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 $24.73   7.547%   $26.5964   $26.60   $26.60   $26.60  
  Purchase #2 $235.61   11.762%   $263.3224   $263.32   $263.30   $263.30  
  Purchase #3 $189.58   8.692%   $206.0583   $206.06   $206.05   $206.10  
  Purchase #4 $202.67   7.416%   $217.7   $217.70   $217.70   $217.70  
  Purchase #5 $83.77   13.584%   $95.1493   $95.15   $95.15   $95.10  
  Purchase #6 $31.63   9.224%   $34.5476   $34.55   $34.55   $34.50  
  Purchase #7 $12.33   3.437%   $12.7538   $12.75   $12.75   $12.80  
  7 purchase totals = $780.32       $856.1278   $856.13   $856.10   $856.10