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 $164.98   12.481%   $185.5712   $185.57   $185.55   $185.60  
  Purchase #2 $157.92   9.841%   $173.4609   $173.46   $173.45   $173.50  
  Purchase #3 $136.29   8.430%   $147.7792   $147.78   $147.80   $147.80  
  Purchase #4 $46.91   13.402%   $53.1969   $53.20   $53.20   $53.20  
  Purchase #5 $26.65   11.771%   $29.787   $29.79   $29.80   $29.80  
  Purchase #6 $117.28   6.215%   $124.569   $124.57   $124.55   $124.60  
  Purchase #7 $44.48   8.852%   $48.4174   $48.42   $48.40   $48.40  
  7 purchase totals = $694.51       $762.7816   $762.79   $762.75   $762.90