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 $235.84   4.839%   $247.2523   $247.25   $247.25   $247.30  
  Purchase #2 $220.38   3.371%   $227.809   $227.81   $227.80   $227.80  
  Purchase #3 $21.81   9.189%   $23.8141   $23.81   $23.80   $23.80  
  Purchase #4 $45.93   7.793%   $49.5093   $49.51   $49.50   $49.50  
  Purchase #5 $147.63   6.322%   $156.9632   $156.96   $156.95   $157.00  
  Purchase #6 $223.75   11.104%   $248.5952   $248.60   $248.60   $248.60  
  Purchase #7 $230.85   5.144%   $242.7249   $242.72   $242.70   $242.70  
  7 purchase totals = $1,126.19       $1,196.6680   $1,196.66   $1,196.60   $1,196.70