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 $249.43   5.464%   $263.0589   $263.06   $263.05   $263.10  
  Purchase #2 $112.58   8.562%   $122.2191   $122.22   $122.20   $122.20  
  Purchase #3 $22.44   4.609%   $23.4743   $23.47   $23.45   $23.50  
  Purchase #4 $223.41   8.717%   $242.8846   $242.88   $242.90   $242.90  
  Purchase #5 $212.57   9.534%   $232.8364   $232.84   $232.85   $232.80  
  Purchase #6 $126.34   11.276%   $140.5861   $140.59   $140.60   $140.60  
  Purchase #7 $234.83   7.838%   $253.236   $253.24   $253.25   $253.20  
  7 purchase totals = $1,181.60       $1,278.2954   $1,278.30   $1,278.30   $1,278.30