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 $204.38   5.381%   $215.3777   $215.38   $215.40   $215.40  
  Purchase #2 $52.48   8.458%   $56.9188   $56.92   $56.90   $56.90  
  Purchase #3 $82.86   10.814%   $91.8205   $91.82   $91.80   $91.80  
  Purchase #4 $183.79   13.144%   $207.9474   $207.95   $207.95   $207.90  
  Purchase #5 $230.40   4.398%   $240.533   $240.53   $240.55   $240.50  
  Purchase #6 $77.97   7.694%   $83.969   $83.97   $83.95   $84.00  
  Purchase #7 $149.35   8.873%   $162.6018   $162.60   $162.60   $162.60  
  7 purchase totals = $981.23       $1,059.1682   $1,059.17   $1,059.15   $1,059.10