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 $195.51   10.272%   $215.5928   $215.59   $215.60   $215.60  
  Purchase #2 $158.67   13.284%   $179.7477   $179.75   $179.75   $179.70  
  Purchase #3 $45.56   8.465%   $49.4167   $49.42   $49.40   $49.40  
  Purchase #4 $203.94   4.200%   $212.5055   $212.51   $212.50   $212.50  
  Purchase #5 $232.65   7.434%   $249.9452   $249.95   $249.95   $249.90  
  Purchase #6 $173.79   10.565%   $192.1509   $192.15   $192.15   $192.20  
  Purchase #7 $130.93   3.770%   $135.8661   $135.87   $135.85   $135.90  
  7 purchase totals = $1,141.05       $1,235.2249   $1,235.24   $1,235.20   $1,235.20