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 $87.28   10.837%   $96.7385   $96.74   $96.75   $96.70  
  Purchase #2 $194.88   7.335%   $209.1744   $209.17   $209.15   $209.20  
  Purchase #3 $41.75   4.620%   $43.6789   $43.68   $43.70   $43.70  
  Purchase #4 $240.65   5.126%   $252.9857   $252.99   $253.00   $253.00  
  Purchase #5 $147.78   3.606%   $153.1089   $153.11   $153.10   $153.10  
  Purchase #6 $85.87   8.868%   $93.485   $93.49   $93.50   $93.50  
  Purchase #7 $231.86   12.225%   $260.2049   $260.20   $260.20   $260.20  
  7 purchase totals = $1,030.07       $1,109.3763   $1,109.38   $1,109.40   $1,109.40