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 $124.79   3.523%   $129.1864   $129.19   $129.20   $129.20  
  Purchase #2 $216.83   12.320%   $243.5435   $243.54   $243.55   $243.50  
  Purchase #3 $27.93   9.187%   $30.4959   $30.50   $30.50   $30.50  
  Purchase #4 $214.35   9.303%   $234.291   $234.29   $234.30   $234.30  
  Purchase #5 $171.76   3.764%   $178.225   $178.23   $178.25   $178.20  
  Purchase #6 $5.85   4.641%   $6.1215   $6.12   $6.10   $6.10  
  Purchase #7 $190.86   10.206%   $210.3392   $210.34   $210.35   $210.30  
  7 purchase totals = $952.37       $1,032.2025   $1,032.21   $1,032.25   $1,032.10