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 $168.84   4.102%   $175.7658   $175.77   $175.75   $175.80  
  Purchase #2 $224.56   7.148%   $240.6115   $240.61   $240.60   $240.60  
  Purchase #3 $220.89   5.570%   $233.1936   $233.19   $233.20   $233.20  
  Purchase #4 $246.96   5.261%   $259.9526   $259.95   $259.95   $260.00  
  Purchase #5 $65.84   11.137%   $73.1726   $73.17   $73.15   $73.20  
  Purchase #6 $43.40   11.561%   $48.4175   $48.42   $48.40   $48.40  
  Purchase #7 $214.55   10.736%   $237.5841   $237.58   $237.60   $237.60  
  7 purchase totals = $1,185.04       $1,268.6977   $1,268.69   $1,268.65   $1,268.80