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 $157.50   7.799%   $169.7834   $169.78   $169.80   $169.80  
  Purchase #2 $148.55   6.529%   $158.2488   $158.25   $158.25   $158.20  
  Purchase #3 $81.48   9.114%   $88.9061   $88.91   $88.90   $88.90  
  Purchase #4 $19.27   8.852%   $20.9758   $20.98   $21.00   $21.00  
  Purchase #5 $77.97   12.850%   $87.9891   $87.99   $88.00   $88.00  
  Purchase #6 $44.95   7.859%   $48.4826   $48.48   $48.50   $48.50  
  Purchase #7 $10.89   8.150%   $11.7775   $11.78   $11.80   $11.80  
  7 purchase totals = $540.61       $586.1633   $586.17   $586.25   $586.20