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 $109.98   7.749%   $118.5024   $118.50   $118.50   $118.50  
  Purchase #2 $130.67   4.728%   $136.8481   $136.85   $136.85   $136.80  
  Purchase #3 $195.98   8.439%   $212.5188   $212.52   $212.50   $212.50  
  Purchase #4 $207.87   7.649%   $223.77   $223.77   $223.75   $223.80  
  Purchase #5 $175.38   13.692%   $199.393   $199.39   $199.40   $199.40  
  Purchase #6 $163.83   10.475%   $180.9912   $180.99   $181.00   $181.00  
  Purchase #7 $142.88   13.575%   $162.276   $162.28   $162.30   $162.30  
  7 purchase totals = $1,126.59       $1,234.2995   $1,234.30   $1,234.30   $1,234.30