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 $81.35   3.800%   $84.4413   $84.44   $84.45   $84.40  
  Purchase #2 $203.65   9.817%   $223.6423   $223.64   $223.65   $223.60  
  Purchase #3 $240.48   11.153%   $267.3007   $267.30   $267.30   $267.30  
  Purchase #4 $14.92   11.103%   $16.5766   $16.58   $16.60   $16.60  
  Purchase #5 $25.90   10.383%   $28.5892   $28.59   $28.60   $28.60  
  Purchase #6 $151.90   4.765%   $159.138   $159.14   $159.15   $159.10  
  Purchase #7 $245.77   11.370%   $273.714   $273.71   $273.70   $273.70  
  7 purchase totals = $963.97       $1,053.4021   $1,053.40   $1,053.45   $1,053.30