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 $172.27   13.547%   $195.6074   $195.61   $195.60   $195.60  
  Purchase #2 $74.35   7.862%   $80.1954   $80.20   $80.20   $80.20  
  Purchase #3 $140.29   4.522%   $146.6339   $146.63   $146.65   $146.60  
  Purchase #4 $134.97   13.798%   $153.5932   $153.59   $153.60   $153.60  
  Purchase #5 $97.97   5.149%   $103.0145   $103.01   $103.00   $103.00  
  Purchase #6 $126.72   12.710%   $142.8261   $142.83   $142.85   $142.80  
  Purchase #7 $245.80   4.724%   $257.4116   $257.41   $257.40   $257.40  
  7 purchase totals = $992.37       $1,079.2821   $1,079.28   $1,079.30   $1,079.20