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 $127.50   5.632%   $134.6808   $134.68   $134.70   $134.70  
  Purchase #2 $171.79   13.702%   $195.3287   $195.33   $195.35   $195.30  
  Purchase #3 $95.93   5.665%   $101.3644   $101.36   $101.35   $101.40  
  Purchase #4 $215.65   9.398%   $235.9168   $235.92   $235.90   $235.90  
  Purchase #5 $225.59   11.649%   $251.869   $251.87   $251.85   $251.90  
  Purchase #6 $46.68   8.824%   $50.799   $50.80   $50.80   $50.80  
  Purchase #7 $24.88   7.311%   $26.699   $26.70   $26.70   $26.70  
  7 purchase totals = $908.02       $996.6577   $996.66   $996.65   $996.70