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 $53.47   12.658%   $60.2382   $60.24   $60.25   $60.20  
  Purchase #2 $235.72   9.184%   $257.3685   $257.37   $257.35   $257.40  
  Purchase #3 $248.85   13.776%   $283.1316   $283.13   $283.15   $283.10  
  Purchase #4 $7.90   6.413%   $8.4066   $8.41   $8.40   $8.40  
  Purchase #5 $201.33   5.642%   $212.689   $212.69   $212.70   $212.70  
  Purchase #6 $127.60   10.217%   $140.6369   $140.64   $140.65   $140.60  
  Purchase #7 $242.67   6.814%   $259.2055   $259.21   $259.20   $259.20  
  7 purchase totals = $1,117.54       $1,221.6763   $1,221.69   $1,221.70   $1,221.60