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 $41.61   13.702%   $47.3114   $47.31   $47.30   $47.30  
  Purchase #2 $23.67   11.321%   $26.3497   $26.35   $26.35   $26.30  
  Purchase #3 $147.55   13.470%   $167.425   $167.43   $167.45   $167.40  
  Purchase #4 $115.49   6.740%   $123.274   $123.27   $123.25   $123.30  
  Purchase #5 $136.72   6.623%   $145.775   $145.78   $145.80   $145.80  
  Purchase #6 $123.43   7.184%   $132.2972   $132.30   $132.30   $132.30  
  Purchase #7 $244.85   5.687%   $258.7746   $258.77   $258.75   $258.80  
  7 purchase totals = $833.32       $901.2069   $901.21   $901.20   $901.20