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 $58.87   7.172%   $63.0922   $63.09   $63.10   $63.10  
  Purchase #2 $111.84   5.345%   $117.8178   $117.82   $117.80   $117.80  
  Purchase #3 $157.70   5.311%   $166.0754   $166.08   $166.10   $166.10  
  Purchase #4 $60.28   4.141%   $62.7762   $62.78   $62.80   $62.80  
  Purchase #5 $14.80   11.386%   $16.4851   $16.49   $16.50   $16.50  
  Purchase #6 $189.63   12.107%   $212.5885   $212.59   $212.60   $212.60  
  Purchase #7 $172.83   7.161%   $185.2064   $185.21   $185.20   $185.20  
  7 purchase totals = $765.95       $824.0416   $824.06   $824.10   $824.10