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 $165.34   11.738%   $184.7476   $184.75   $184.75   $184.70  
  Purchase #2 $246.63   11.857%   $275.8729   $275.87   $275.85   $275.90  
  Purchase #3 $127.37   6.863%   $136.1114   $136.11   $136.10   $136.10  
  Purchase #4 $75.82   10.115%   $83.4892   $83.49   $83.50   $83.50  
  Purchase #5 $179.87   10.496%   $198.7492   $198.75   $198.75   $198.70  
  Purchase #6 $223.29   8.287%   $241.794   $241.79   $241.80   $241.80  
  Purchase #7 $241.51   11.184%   $268.5205   $268.52   $268.50   $268.50  
  7 purchase totals = $1,259.83       $1,389.2848   $1,389.28   $1,389.25   $1,389.20