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 $131.95   3.698%   $136.8295   $136.83   $136.85   $136.80  
  Purchase #2 $250.52   7.323%   $268.8656   $268.87   $268.85   $268.90  
  Purchase #3 $202.37   13.712%   $230.119   $230.12   $230.10   $230.10  
  Purchase #4 $60.99   5.835%   $64.5488   $64.55   $64.55   $64.50  
  Purchase #5 $67.99   5.340%   $71.6207   $71.62   $71.60   $71.60  
  Purchase #6 $239.94   4.244%   $250.1231   $250.12   $250.10   $250.10  
  Purchase #7 $84.67   8.746%   $92.0752   $92.08   $92.10   $92.10  
  7 purchase totals = $1,038.43       $1,114.1819   $1,114.19   $1,114.15   $1,114.10