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 $237.55   5.227%   $249.9667   $249.97   $249.95   $250.00  
  Purchase #2 $68.32   3.404%   $70.6456   $70.65   $70.65   $70.60  
  Purchase #3 $219.80   4.175%   $228.9767   $228.98   $229.00   $229.00  
  Purchase #4 $90.45   6.600%   $96.4197   $96.42   $96.40   $96.40  
  Purchase #5 $143.64   6.152%   $152.4767   $152.48   $152.50   $152.50  
  Purchase #6 $19.28   5.825%   $20.4031   $20.40   $20.40   $20.40  
  Purchase #7 $231.44   4.276%   $241.3364   $241.34   $241.35   $241.30  
  7 purchase totals = $1,010.48       $1,060.2249   $1,060.24   $1,060.25   $1,060.20