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 $241.26   12.301%   $270.9374   $270.94   $270.95   $270.90  
  Purchase #2 $95.74   9.416%   $104.7549   $104.75   $104.75   $104.80  
  Purchase #3 $192.55   12.796%   $217.1887   $217.19   $217.20   $217.20  
  Purchase #4 $139.45   10.715%   $154.3921   $154.39   $154.40   $154.40  
  Purchase #5 $183.37   5.703%   $193.8276   $193.83   $193.85   $193.80  
  Purchase #6 $61.41   6.619%   $65.4747   $65.47   $65.45   $65.50  
  Purchase #7 $181.58   7.399%   $195.0151   $195.02   $195.00   $195.00  
  7 purchase totals = $1,095.36       $1,201.5905   $1,201.59   $1,201.60   $1,201.60