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 $205.89   8.748%   $223.9013   $223.90   $223.90   $223.90  
  Purchase #2 $160.84   9.850%   $176.6827   $176.68   $176.70   $176.70  
  Purchase #3 $72.67   11.186%   $80.7989   $80.80   $80.80   $80.80  
  Purchase #4 $106.36   6.549%   $113.3255   $113.33   $113.35   $113.30  
  Purchase #5 $184.67   13.449%   $209.5063   $209.51   $209.50   $209.50  
  Purchase #6 $130.61   3.613%   $135.3289   $135.33   $135.35   $135.30  
  Purchase #7 $76.42   9.458%   $83.6478   $83.65   $83.65   $83.60  
  7 purchase totals = $937.46       $1,023.1914   $1,023.20   $1,023.25   $1,023.10