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 $219.96   4.604%   $230.087   $230.09   $230.10   $230.10  
  Purchase #2 $192.77   5.392%   $203.1642   $203.16   $203.15   $203.20  
  Purchase #3 $38.62   13.812%   $43.9542   $43.95   $43.95   $44.00  
  Purchase #4 $28.48   6.866%   $30.4354   $30.44   $30.45   $30.40  
  Purchase #5 $150.81   13.654%   $171.4016   $171.40   $171.40   $171.40  
  Purchase #6 $59.97   9.311%   $65.5538   $65.55   $65.55   $65.60  
  Purchase #7 $203.34   3.192%   $209.8306   $209.83   $209.85   $209.80  
  7 purchase totals = $893.95       $954.4268   $954.42   $954.45   $954.50