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 $209.94   6.487%   $223.5588   $223.56   $223.55   $223.60  
  Purchase #2 $56.92   5.286%   $59.9288   $59.93   $59.95   $59.90  
  Purchase #3 $123.98   4.120%   $129.088   $129.09   $129.10   $129.10  
  Purchase #4 $178.54   10.588%   $197.4438   $197.44   $197.45   $197.40  
  Purchase #5 $250.67   4.854%   $262.8375   $262.84   $262.85   $262.80  
  Purchase #6 $240.70   9.775%   $264.2284   $264.23   $264.25   $264.20  
  Purchase #7 $63.61   3.754%   $65.9979   $66.00   $66.00   $66.00  
  7 purchase totals = $1,124.36       $1,203.0832   $1,203.09   $1,203.15   $1,203.00