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 $69.30   11.301%   $77.1316   $77.13   $77.15   $77.10  
  Purchase #2 $101.99   12.428%   $114.6653   $114.67   $114.65   $114.70  
  Purchase #3 $133.93   3.356%   $138.4247   $138.42   $138.40   $138.40  
  Purchase #4 $123.62   10.621%   $136.7497   $136.75   $136.75   $136.70  
  Purchase #5 $59.33   10.206%   $65.3852   $65.39   $65.40   $65.40  
  Purchase #6 $231.75   3.192%   $239.1475   $239.15   $239.15   $239.10  
  Purchase #7 $166.26   9.835%   $182.6117   $182.61   $182.60   $182.60  
  7 purchase totals = $886.18       $954.1157   $954.12   $954.10   $954.00