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 $55.75   10.467%   $61.5854   $61.59   $61.60   $61.60  
  Purchase #2 $225.41   6.438%   $239.9219   $239.92   $239.90   $239.90  
  Purchase #3 $181.44   12.204%   $203.5829   $203.58   $203.60   $203.60  
  Purchase #4 $168.25   11.368%   $187.3767   $187.38   $187.40   $187.40  
  Purchase #5 $128.80   13.740%   $146.4971   $146.50   $146.50   $146.50  
  Purchase #6 $24.48   4.343%   $25.5432   $25.54   $25.55   $25.50  
  Purchase #7 $195.93   3.796%   $203.3675   $203.37   $203.35   $203.40  
  7 purchase totals = $980.06       $1,067.8747   $1,067.88   $1,067.90   $1,067.90