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 $50.68   11.780%   $56.6501   $56.65   $56.65   $56.70  
  Purchase #2 $247.78   10.649%   $274.1661   $274.17   $274.15   $274.20  
  Purchase #3 $208.72   4.825%   $218.7907   $218.79   $218.80   $218.80  
  Purchase #4 $189.29   11.601%   $211.2495   $211.25   $211.25   $211.20  
  Purchase #5 $202.65   10.164%   $223.2473   $223.25   $223.25   $223.20  
  Purchase #6 $225.96   6.169%   $239.8995   $239.90   $239.90   $239.90  
  Purchase #7 $53.83   7.185%   $57.6977   $57.70   $57.70   $57.70  
  7 purchase totals = $1,178.91       $1,281.7009   $1,281.71   $1,281.70   $1,281.70