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 $204.53   13.370%   $231.8757   $231.88   $231.90   $231.90  
  Purchase #2 $85.59   11.427%   $95.3704   $95.37   $95.35   $95.40  
  Purchase #3 $111.84   6.660%   $119.2885   $119.29   $119.30   $119.30  
  Purchase #4 $243.70   7.146%   $261.1148   $261.11   $261.10   $261.10  
  Purchase #5 $33.42   4.463%   $34.9115   $34.91   $34.90   $34.90  
  Purchase #6 $162.29   12.682%   $182.8716   $182.87   $182.85   $182.90  
  Purchase #7 $186.52   3.368%   $192.802   $192.80   $192.80   $192.80  
  7 purchase totals = $1,027.89       $1,118.2345   $1,118.23   $1,118.20   $1,118.30