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 $112.35   5.263%   $118.263   $118.26   $118.25   $118.30  
  Purchase #2 $49.63   8.723%   $53.9592   $53.96   $53.95   $54.00  
  Purchase #3 $228.86   4.212%   $238.4996   $238.50   $238.50   $238.50  
  Purchase #4 $233.62   9.140%   $254.9729   $254.97   $254.95   $255.00  
  Purchase #5 $231.68   4.307%   $241.6585   $241.66   $241.65   $241.70  
  Purchase #6 $201.82   8.369%   $218.7103   $218.71   $218.70   $218.70  
  Purchase #7 $105.33   3.586%   $109.1071   $109.11   $109.10   $109.10  
  7 purchase totals = $1,163.29       $1,235.1706   $1,235.17   $1,235.10   $1,235.30