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 $66.41   7.696%   $71.5209   $71.52   $71.50   $71.50  
  Purchase #2 $248.75   3.718%   $257.9985   $258.00   $258.00   $258.00  
  Purchase #3 $247.81   7.228%   $265.7217   $265.72   $265.70   $265.70  
  Purchase #4 $231.99   9.574%   $254.2007   $254.20   $254.20   $254.20  
  Purchase #5 $209.60   5.458%   $221.04   $221.04   $221.05   $221.00  
  Purchase #6 $59.41   9.449%   $65.0237   $65.02   $65.00   $65.00  
  Purchase #7 $160.98   4.852%   $168.7907   $168.79   $168.80   $168.80  
  7 purchase totals = $1,224.95       $1,304.2962   $1,304.29   $1,304.25   $1,304.20