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 $188.51   6.614%   $200.9781   $200.98   $201.00   $201.00  
  Purchase #2 $49.25   13.800%   $56.0465   $56.05   $56.05   $56.00  
  Purchase #3 $39.34   12.483%   $44.2508   $44.25   $44.25   $44.30  
  Purchase #4 $75.91   12.166%   $85.1452   $85.15   $85.15   $85.10  
  Purchase #5 $93.65   11.843%   $104.741   $104.74   $104.75   $104.70  
  Purchase #6 $224.40   4.183%   $233.7867   $233.79   $233.80   $233.80  
  Purchase #7 $48.50   5.484%   $51.1597   $51.16   $51.15   $51.20  
  7 purchase totals = $719.56       $776.1080   $776.12   $776.15   $776.10