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 $91.33   4.756%   $95.6737   $95.67   $95.65   $95.70  
  Purchase #2 $25.89   9.409%   $28.326   $28.33   $28.35   $28.30  
  Purchase #3 $124.44   7.207%   $133.4084   $133.41   $133.40   $133.40  
  Purchase #4 $38.76   6.798%   $41.3949   $41.39   $41.40   $41.40  
  Purchase #5 $224.91   4.703%   $235.4875   $235.49   $235.50   $235.50  
  Purchase #6 $162.31   8.573%   $176.2248   $176.22   $176.20   $176.20  
  Purchase #7 $184.85   12.773%   $208.4609   $208.46   $208.45   $208.50  
  7 purchase totals = $852.49       $918.9762   $918.97   $918.95   $919.00