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 $166.38   5.475%   $175.4893   $175.49   $175.50   $175.50  
  Purchase #2 $92.27   4.699%   $96.6058   $96.61   $96.60   $96.60  
  Purchase #3 $248.34   9.559%   $272.0788   $272.08   $272.10   $272.10  
  Purchase #4 $53.76   5.793%   $56.8743   $56.87   $56.85   $56.90  
  Purchase #5 $218.34   12.311%   $245.2198   $245.22   $245.20   $245.20  
  Purchase #6 $59.60   9.332%   $65.1619   $65.16   $65.15   $65.20  
  Purchase #7 $97.30   13.618%   $110.5503   $110.55   $110.55   $110.60  
  7 purchase totals = $935.99       $1,021.9802   $1,021.98   $1,021.95   $1,022.10