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 $54.49   11.346%   $60.6724   $60.67   $60.65   $60.70  
  Purchase #2 $226.64   6.390%   $241.1223   $241.12   $241.10   $241.10  
  Purchase #3 $176.36   13.856%   $200.7964   $200.80   $200.80   $200.80  
  Purchase #4 $235.48   7.130%   $252.2697   $252.27   $252.25   $252.30  
  Purchase #5 $118.80   8.534%   $128.9384   $128.94   $128.95   $128.90  
  Purchase #6 $176.82   12.360%   $198.675   $198.68   $198.70   $198.70  
  Purchase #7 $247.56   8.324%   $268.1669   $268.17   $268.15   $268.20  
  7 purchase totals = $1,236.15       $1,350.6411   $1,350.65   $1,350.60   $1,350.70