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 $231.34   4.457%   $241.6508   $241.65   $241.65   $241.70  
  Purchase #2 $22.77   7.779%   $24.5413   $24.54   $24.55   $24.50  
  Purchase #3 $246.40   7.432%   $264.7124   $264.71   $264.70   $264.70  
  Purchase #4 $130.89   8.768%   $142.3664   $142.37   $142.35   $142.40  
  Purchase #5 $180.40   13.236%   $204.2777   $204.28   $204.30   $204.30  
  Purchase #6 $137.97   8.177%   $149.2518   $149.25   $149.25   $149.30  
  Purchase #7 $161.61   8.856%   $175.9222   $175.92   $175.90   $175.90  
  7 purchase totals = $1,111.38       $1,202.7226   $1,202.72   $1,202.70   $1,202.80