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 $216.94   11.363%   $241.5909   $241.59   $241.60   $241.60  
  Purchase #2 $117.84   13.551%   $133.8085   $133.81   $133.80   $133.80  
  Purchase #3 $84.29   13.112%   $95.3421   $95.34   $95.35   $95.30  
  Purchase #4 $202.90   7.457%   $218.0303   $218.03   $218.05   $218.00  
  Purchase #5 $79.38   10.292%   $87.5498   $87.55   $87.55   $87.50  
  Purchase #6 $16.85   3.111%   $17.3742   $17.37   $17.35   $17.40  
  Purchase #7 $78.53   13.716%   $89.3012   $89.30   $89.30   $89.30  
  7 purchase totals = $796.73       $882.9970   $882.99   $883.00   $882.90