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 $194.91   6.423%   $207.4291   $207.43   $207.45   $207.40  
  Purchase #2 $25.90   6.559%   $27.5988   $27.60   $27.60   $27.60  
  Purchase #3 $240.77   7.145%   $257.973   $257.97   $257.95   $258.00  
  Purchase #4 $228.97   10.740%   $253.5614   $253.56   $253.55   $253.60  
  Purchase #5 $167.30   8.643%   $181.7597   $181.76   $181.75   $181.80  
  Purchase #6 $28.76   5.250%   $30.2699   $30.27   $30.25   $30.30  
  Purchase #7 $85.77   5.277%   $90.2961   $90.30   $90.30   $90.30  
  7 purchase totals = $972.38       $1,048.8880   $1,048.89   $1,048.85   $1,049.00