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 $214.51   8.301%   $232.3165   $232.32   $232.30   $232.30  
  Purchase #2 $116.51   10.578%   $128.8344   $128.83   $128.85   $128.80  
  Purchase #3 $30.90   12.500%   $34.7625   $34.76   $34.75   $34.80  
  Purchase #4 $193.84   4.762%   $203.0707   $203.07   $203.05   $203.10  
  Purchase #5 $242.28   11.855%   $271.0023   $271.00   $271.00   $271.00  
  Purchase #6 $165.42   9.812%   $181.651   $181.65   $181.65   $181.70  
  Purchase #7 $206.25   13.843%   $234.8012   $234.80   $234.80   $234.80  
  7 purchase totals = $1,169.71       $1,286.4386   $1,286.43   $1,286.40   $1,286.50