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 $138.89   9.656%   $152.3012   $152.30   $152.30   $152.30  
  Purchase #2 $63.45   3.332%   $65.5642   $65.56   $65.55   $65.60  
  Purchase #3 $87.93   11.358%   $97.9171   $97.92   $97.90   $97.90  
  Purchase #4 $82.33   13.608%   $93.5335   $93.53   $93.55   $93.50  
  Purchase #5 $224.49   6.480%   $239.037   $239.04   $239.05   $239.00  
  Purchase #6 $167.97   5.243%   $176.7767   $176.78   $176.80   $176.80  
  Purchase #7 $192.42   12.543%   $216.5552   $216.56   $216.55   $216.60  
  7 purchase totals = $957.48       $1,041.6849   $1,041.69   $1,041.70   $1,041.70