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 $29.73   9.816%   $32.6483   $32.65   $32.65   $32.60  
  Purchase #2 $166.48   5.514%   $175.6597   $175.66   $175.65   $175.70  
  Purchase #3 $18.43   4.635%   $19.2842   $19.28   $19.30   $19.30  
  Purchase #4 $218.32   3.726%   $226.4546   $226.45   $226.45   $226.50  
  Purchase #5 $145.51   7.318%   $156.1584   $156.16   $156.15   $156.20  
  Purchase #6 $243.33   9.334%   $266.0424   $266.04   $266.05   $266.00  
  Purchase #7 $228.86   7.222%   $245.3883   $245.39   $245.40   $245.40  
  7 purchase totals = $1,050.66       $1,121.6359   $1,121.63   $1,121.65   $1,121.70