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 $79.41   3.217%   $81.9646   $81.96   $81.95   $82.00  
  Purchase #2 $37.99   10.206%   $41.8673   $41.87   $41.85   $41.90  
  Purchase #3 $163.33   7.405%   $175.4246   $175.42   $175.40   $175.40  
  Purchase #4 $158.65   8.129%   $171.5467   $171.55   $171.55   $171.50  
  Purchase #5 $184.34   11.132%   $204.8607   $204.86   $204.85   $204.90  
  Purchase #6 $220.76   9.502%   $241.7366   $241.74   $241.75   $241.70  
  Purchase #7 $88.99   4.397%   $92.9029   $92.90   $92.90   $92.90  
  7 purchase totals = $933.47       $1,010.3034   $1,010.30   $1,010.25   $1,010.30