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 $194.67   6.156%   $206.6539   $206.65   $206.65   $206.70  
  Purchase #2 $41.38   7.555%   $44.5063   $44.51   $44.50   $44.50  
  Purchase #3 $215.99   13.552%   $245.261   $245.26   $245.25   $245.30  
  Purchase #4 $120.40   11.693%   $134.4784   $134.48   $134.50   $134.50  
  Purchase #5 $30.61   3.782%   $31.7677   $31.77   $31.75   $31.80  
  Purchase #6 $158.49   5.505%   $167.2149   $167.21   $167.20   $167.20  
  Purchase #7 $211.53   6.160%   $224.5602   $224.56   $224.55   $224.60  
  7 purchase totals = $973.07       $1,054.4424   $1,054.44   $1,054.40   $1,054.60