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 $226.87   11.131%   $252.1229   $252.12   $252.10   $252.10  
  Purchase #2 $142.75   7.148%   $152.9538   $152.95   $152.95   $153.00  
  Purchase #3 $187.84   5.520%   $198.2088   $198.21   $198.20   $198.20  
  Purchase #4 $243.60   4.189%   $253.8044   $253.80   $253.80   $253.80  
  Purchase #5 $218.92   3.201%   $225.9276   $225.93   $225.95   $225.90  
  Purchase #6 $142.50   6.595%   $151.8979   $151.90   $151.90   $151.90  
  Purchase #7 $38.54   6.214%   $40.9349   $40.93   $40.95   $40.90  
  7 purchase totals = $1,201.02       $1,275.8503   $1,275.84   $1,275.85   $1,275.80