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 $96.57   12.122%   $108.2762   $108.28   $108.30   $108.30  
  Purchase #2 $57.26   6.111%   $60.7592   $60.76   $60.75   $60.80  
  Purchase #3 $164.40   13.806%   $187.0971   $187.10   $187.10   $187.10  
  Purchase #4 $148.83   13.246%   $168.544   $168.54   $168.55   $168.50  
  Purchase #5 $171.35   6.593%   $182.6471   $182.65   $182.65   $182.60  
  Purchase #6 $87.87   11.743%   $98.1886   $98.19   $98.20   $98.20  
  Purchase #7 $199.31   5.644%   $210.5591   $210.56   $210.55   $210.60  
  7 purchase totals = $925.59       $1,016.0713   $1,016.08   $1,016.10   $1,016.10