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 $144.64   11.702%   $161.5658   $161.57   $161.55   $161.60  
  Purchase #2 $197.79   6.769%   $211.1784   $211.18   $211.20   $211.20  
  Purchase #3 $199.55   13.592%   $226.6728   $226.67   $226.65   $226.70  
  Purchase #4 $43.72   13.767%   $49.7389   $49.74   $49.75   $49.70  
  Purchase #5 $163.38   9.319%   $178.6054   $178.61   $178.60   $178.60  
  Purchase #6 $215.65   9.697%   $236.5616   $236.56   $236.55   $236.60  
  Purchase #7 $180.79   5.226%   $190.2381   $190.24   $190.25   $190.20  
  7 purchase totals = $1,145.52       $1,254.5610   $1,254.57   $1,254.55   $1,254.60