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 $14.84   8.472%   $16.0972   $16.10   $16.10   $16.10  
  Purchase #2 $213.94   10.328%   $236.0357   $236.04   $236.05   $236.00  
  Purchase #3 $240.64   11.108%   $267.3703   $267.37   $267.35   $267.40  
  Purchase #4 $46.96   5.574%   $49.5776   $49.58   $49.60   $49.60  
  Purchase #5 $32.61   13.868%   $37.1324   $37.13   $37.15   $37.10  
  Purchase #6 $216.73   6.270%   $230.319   $230.32   $230.30   $230.30  
  Purchase #7 $120.65   13.554%   $137.0029   $137.00   $137.00   $137.00  
  7 purchase totals = $886.37       $973.5351   $973.54   $973.55   $973.50