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 $205.41   13.790%   $233.736   $233.74   $233.75   $233.70  
  Purchase #2 $7.30   3.818%   $7.5787   $7.58   $7.60   $7.60  
  Purchase #3 $213.66   13.822%   $243.1921   $243.19   $243.20   $243.20  
  Purchase #4 $187.88   11.473%   $209.4355   $209.44   $209.45   $209.40  
  Purchase #5 $17.40   12.778%   $19.6234   $19.62   $19.60   $19.60  
  Purchase #6 $224.88   12.801%   $253.6669   $253.67   $253.65   $253.70  
  Purchase #7 $50.82   12.239%   $57.0399   $57.04   $57.05   $57.00  
  7 purchase totals = $907.35       $1,024.2725   $1,024.28   $1,024.30   $1,024.20