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 $69.33   9.111%   $75.6467   $75.65   $75.65   $75.60  
  Purchase #2 $66.65   4.636%   $69.7399   $69.74   $69.75   $69.70  
  Purchase #3 $108.36   4.202%   $112.9133   $112.91   $112.90   $112.90  
  Purchase #4 $177.72   13.299%   $201.355   $201.36   $201.35   $201.40  
  Purchase #5 $66.61   10.125%   $73.3543   $73.35   $73.35   $73.40  
  Purchase #6 $138.92   12.367%   $156.1002   $156.10   $156.10   $156.10  
  Purchase #7 $58.44   5.483%   $61.6443   $61.64   $61.65   $61.60  
  7 purchase totals = $686.03       $750.7537   $750.75   $750.75   $750.70