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 $241.74   4.348%   $252.2509   $252.25   $252.25   $252.30  
  Purchase #2 $70.37   7.373%   $75.5584   $75.56   $75.55   $75.60  
  Purchase #3 $114.81   12.457%   $129.1119   $129.11   $129.10   $129.10  
  Purchase #4 $24.35   5.627%   $25.7202   $25.72   $25.70   $25.70  
  Purchase #5 $198.76   10.735%   $220.0969   $220.10   $220.10   $220.10  
  Purchase #6 $56.51   7.446%   $60.7177   $60.72   $60.70   $60.70  
  Purchase #7 $101.50   9.229%   $110.8674   $110.87   $110.85   $110.90  
  7 purchase totals = $808.04       $874.3234   $874.33   $874.25   $874.40