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 $191.52   11.760%   $214.0428   $214.04   $214.05   $214.00  
  Purchase #2 $61.93   4.503%   $64.7187   $64.72   $64.70   $64.70  
  Purchase #3 $50.74   4.598%   $53.073   $53.07   $53.05   $53.10  
  Purchase #4 $157.88   12.776%   $178.0507   $178.05   $178.05   $178.10  
  Purchase #5 $86.57   10.246%   $95.44   $95.44   $95.45   $95.40  
  Purchase #6 $221.82   8.406%   $240.4662   $240.47   $240.45   $240.50  
  Purchase #7 $89.28   6.243%   $94.8538   $94.85   $94.85   $94.90  
  7 purchase totals = $859.74       $940.6452   $940.64   $940.60   $940.70