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 $65.84   7.346%   $70.6766   $70.68   $70.70   $70.70  
  Purchase #2 $236.27   5.318%   $248.8348   $248.83   $248.85   $248.80  
  Purchase #3 $38.71   9.273%   $42.2996   $42.30   $42.30   $42.30  
  Purchase #4 $93.57   7.685%   $100.7609   $100.76   $100.75   $100.80  
  Purchase #5 $57.56   4.502%   $60.1514   $60.15   $60.15   $60.20  
  Purchase #6 $202.29   12.865%   $228.3146   $228.31   $228.30   $228.30  
  Purchase #7 $15.31   3.127%   $15.7887   $15.79   $15.80   $15.80  
  7 purchase totals = $709.55       $766.8266   $766.82   $766.85   $766.90