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 $59.77   5.730%   $63.1948   $63.19   $63.20   $63.20  
  Purchase #2 $205.57   6.543%   $219.0204   $219.02   $219.00   $219.00  
  Purchase #3 $202.61   7.697%   $218.2049   $218.20   $218.20   $218.20  
  Purchase #4 $88.97   5.276%   $93.6641   $93.66   $93.65   $93.70  
  Purchase #5 $206.71   11.187%   $229.8346   $229.83   $229.85   $229.80  
  Purchase #6 $117.31   13.871%   $133.5821   $133.58   $133.60   $133.60  
  Purchase #7 $71.32   10.209%   $78.6011   $78.60   $78.60   $78.60  
  7 purchase totals = $952.26       $1,036.1020   $1,036.08   $1,036.10   $1,036.10