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 $82.96   13.570%   $94.2177   $94.22   $94.20   $94.20  
  Purchase #2 $89.93   12.703%   $101.3538   $101.35   $101.35   $101.40  
  Purchase #3 $248.64   7.561%   $267.4397   $267.44   $267.45   $267.40  
  Purchase #4 $156.70   9.129%   $171.0051   $171.01   $171.00   $171.00  
  Purchase #5 $48.44   5.340%   $51.0267   $51.03   $51.05   $51.00  
  Purchase #6 $222.28   9.850%   $244.1746   $244.17   $244.15   $244.20  
  Purchase #7 $241.49   6.489%   $257.1603   $257.16   $257.15   $257.20  
  7 purchase totals = $1,090.44       $1,186.3779   $1,186.38   $1,186.35   $1,186.40