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 $208.44   7.163%   $223.3706   $223.37   $223.35   $223.40  
  Purchase #2 $58.40   9.427%   $63.9054   $63.91   $63.90   $63.90  
  Purchase #3 $81.72   6.293%   $86.8626   $86.86   $86.85   $86.90  
  Purchase #4 $207.51   12.124%   $232.6685   $232.67   $232.65   $232.70  
  Purchase #5 $48.44   8.155%   $52.3903   $52.39   $52.40   $52.40  
  Purchase #6 $214.47   11.249%   $238.5957   $238.60   $238.60   $238.60  
  Purchase #7 $78.95   6.251%   $83.8852   $83.89   $83.90   $83.90  
  7 purchase totals = $897.93       $981.6783   $981.69   $981.65   $981.80