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 $219.66   4.415%   $229.358   $229.36   $229.35   $229.40  
  Purchase #2 $134.89   4.523%   $140.9911   $140.99   $141.00   $141.00  
  Purchase #3 $220.39   13.225%   $249.5366   $249.54   $249.55   $249.50  
  Purchase #4 $99.43   9.784%   $109.1582   $109.16   $109.15   $109.20  
  Purchase #5 $203.35   10.642%   $224.9905   $224.99   $225.00   $225.00  
  Purchase #6 $171.51   3.830%   $178.0788   $178.08   $178.10   $178.10  
  Purchase #7 $138.52   13.521%   $157.2493   $157.25   $157.25   $157.20  
  7 purchase totals = $1,187.75       $1,289.3625   $1,289.37   $1,289.40   $1,289.40