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 $246.49   12.218%   $276.6061   $276.61   $276.60   $276.60  
  Purchase #2 $163.58   11.160%   $181.8355   $181.84   $181.85   $181.80  
  Purchase #3 $224.89   4.322%   $234.6097   $234.61   $234.60   $234.60  
  Purchase #4 $167.55   12.311%   $188.1771   $188.18   $188.20   $188.20  
  Purchase #5 $59.98   4.331%   $62.5777   $62.58   $62.60   $62.60  
  Purchase #6 $29.34   4.347%   $30.6154   $30.62   $30.60   $30.60  
  Purchase #7 $204.74   12.136%   $229.5872   $229.59   $229.60   $229.60  
  7 purchase totals = $1,096.57       $1,204.0087   $1,204.03   $1,204.05   $1,204.00