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 $237.72   12.568%   $267.5966   $267.60   $267.60   $267.60  
  Purchase #2 $91.44   13.243%   $103.5494   $103.55   $103.55   $103.50  
  Purchase #3 $86.62   11.834%   $96.8706   $96.87   $96.85   $96.90  
  Purchase #4 $13.42   12.471%   $15.0936   $15.09   $15.10   $15.10  
  Purchase #5 $108.55   8.191%   $117.4413   $117.44   $117.45   $117.40  
  Purchase #6 $236.92   5.585%   $250.152   $250.15   $250.15   $250.20  
  Purchase #7 $167.80   3.674%   $173.965   $173.97   $173.95   $174.00  
  7 purchase totals = $942.47       $1,024.6685   $1,024.67   $1,024.65   $1,024.70