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 $225.61   3.454%   $233.4026   $233.40   $233.40   $233.40  
  Purchase #2 $24.47   11.523%   $27.2897   $27.29   $27.30   $27.30  
  Purchase #3 $52.57   7.367%   $56.4428   $56.44   $56.45   $56.40  
  Purchase #4 $160.66   5.610%   $169.673   $169.67   $169.65   $169.70  
  Purchase #5 $177.74   13.376%   $201.5145   $201.51   $201.50   $201.50  
  Purchase #6 $230.69   8.498%   $250.294   $250.29   $250.30   $250.30  
  Purchase #7 $55.33   13.213%   $62.6408   $62.64   $62.65   $62.60  
  7 purchase totals = $927.07       $1,001.2574   $1,001.24   $1,001.25   $1,001.20