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 $229.32   10.411%   $253.1945   $253.19   $253.20   $253.20  
  Purchase #2 $52.83   7.374%   $56.7257   $56.73   $56.75   $56.70  
  Purchase #3 $81.31   7.299%   $87.2448   $87.24   $87.25   $87.20  
  Purchase #4 $120.55   5.404%   $127.0645   $127.06   $127.05   $127.10  
  Purchase #5 $85.33   6.241%   $90.6554   $90.66   $90.65   $90.70  
  Purchase #6 $250.78   7.338%   $269.1822   $269.18   $269.20   $269.20  
  Purchase #7 $59.99   13.551%   $68.1192   $68.12   $68.10   $68.10  
  7 purchase totals = $880.11       $952.1863   $952.18   $952.20   $952.20