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 $196.67   4.166%   $204.8633   $204.86   $204.85   $204.90  
  Purchase #2 $219.30   8.617%   $238.1971   $238.20   $238.20   $238.20  
  Purchase #3 $236.59   7.356%   $253.9936   $253.99   $254.00   $254.00  
  Purchase #4 $80.58   7.331%   $86.4873   $86.49   $86.50   $86.50  
  Purchase #5 $85.25   11.397%   $94.9659   $94.97   $94.95   $95.00  
  Purchase #6 $56.82   13.163%   $64.2992   $64.30   $64.30   $64.30  
  Purchase #7 $239.64   6.319%   $254.7829   $254.78   $254.80   $254.80  
  7 purchase totals = $1,114.85       $1,197.5893   $1,197.59   $1,197.60   $1,197.70