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 $52.49   12.701%   $59.1568   $59.16   $59.15   $59.20  
  Purchase #2 $213.32   7.692%   $229.7286   $229.73   $229.75   $229.70  
  Purchase #3 $153.35   5.661%   $162.0311   $162.03   $162.05   $162.00  
  Purchase #4 $164.66   11.809%   $184.1047   $184.10   $184.10   $184.10  
  Purchase #5 $145.60   7.169%   $156.0381   $156.04   $156.05   $156.00  
  Purchase #6 $159.50   11.443%   $177.7516   $177.75   $177.75   $177.80  
  Purchase #7 $225.87   9.659%   $247.6868   $247.69   $247.70   $247.70  
  7 purchase totals = $1,114.79       $1,216.4977   $1,216.50   $1,216.55   $1,216.50