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 $174.95   3.115%   $180.3997   $180.40   $180.40   $180.40  
  Purchase #2 $203.98   4.110%   $212.3636   $212.36   $212.35   $212.40  
  Purchase #3 $27.56   8.582%   $29.9252   $29.93   $29.95   $29.90  
  Purchase #4 $195.58   3.337%   $202.1065   $202.11   $202.10   $202.10  
  Purchase #5 $44.76   9.634%   $49.0722   $49.07   $49.05   $49.10  
  Purchase #6 $187.56   4.317%   $195.657   $195.66   $195.65   $195.70  
  Purchase #7 $134.96   5.311%   $142.1277   $142.13   $142.15   $142.10  
  7 purchase totals = $969.35       $1,011.6519   $1,011.66   $1,011.65   $1,011.70