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 $184.98   10.383%   $204.1865   $204.19   $204.20   $204.20  
  Purchase #2 $153.42   13.727%   $174.48   $174.48   $174.50   $174.50  
  Purchase #3 $205.34   6.628%   $218.9499   $218.95   $218.95   $218.90  
  Purchase #4 $232.89   5.316%   $245.2704   $245.27   $245.25   $245.30  
  Purchase #5 $194.86   8.634%   $211.6842   $211.68   $211.70   $211.70  
  Purchase #6 $233.83   10.461%   $258.291   $258.29   $258.30   $258.30  
  Purchase #7 $26.53   13.540%   $30.1222   $30.12   $30.10   $30.10  
  7 purchase totals = $1,231.85       $1,342.9842   $1,342.98   $1,343.00   $1,343.00