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 $54.28   12.204%   $60.9043   $60.90   $60.90   $60.90  
  Purchase #2 $189.92   3.533%   $196.6299   $196.63   $196.65   $196.60  
  Purchase #3 $202.57   4.298%   $211.2765   $211.28   $211.30   $211.30  
  Purchase #4 $36.27   12.823%   $40.9209   $40.92   $40.90   $40.90  
  Purchase #5 $220.89   6.681%   $235.6477   $235.65   $235.65   $235.60  
  Purchase #6 $206.40   11.745%   $230.6417   $230.64   $230.65   $230.60  
  Purchase #7 $201.99   9.727%   $221.6376   $221.64   $221.65   $221.60  
  7 purchase totals = $1,112.32       $1,197.6586   $1,197.66   $1,197.70   $1,197.50