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 $77.48   8.546%   $84.1014   $84.10   $84.10   $84.10  
  Purchase #2 $191.65   5.620%   $202.4207   $202.42   $202.40   $202.40  
  Purchase #3 $30.42   9.688%   $33.3671   $33.37   $33.35   $33.40  
  Purchase #4 $236.90   12.779%   $267.1735   $267.17   $267.15   $267.20  
  Purchase #5 $222.77   12.841%   $251.3759   $251.38   $251.40   $251.40  
  Purchase #6 $187.68   11.664%   $209.571   $209.57   $209.55   $209.60  
  Purchase #7 $122.38   13.687%   $139.1302   $139.13   $139.15   $139.10  
  7 purchase totals = $1,069.28       $1,187.1398   $1,187.14   $1,187.10   $1,187.20