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 $133.62   9.202%   $145.9157   $145.92   $145.90   $145.90  
  Purchase #2 $56.65   13.278%   $64.172   $64.17   $64.15   $64.20  
  Purchase #3 $81.50   9.487%   $89.2319   $89.23   $89.25   $89.20  
  Purchase #4 $230.36   8.527%   $250.0028   $250.00   $250.00   $250.00  
  Purchase #5 $125.88   5.499%   $132.8021   $132.80   $132.80   $132.80  
  Purchase #6 $218.90   10.377%   $241.6153   $241.62   $241.60   $241.60  
  Purchase #7 $94.27   7.677%   $101.5071   $101.51   $101.50   $101.50  
  7 purchase totals = $941.18       $1,025.2469   $1,025.25   $1,025.20   $1,025.20