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 $36.58   13.681%   $41.5845   $41.58   $41.60   $41.60  
  Purchase #2 $214.55   13.277%   $243.0358   $243.04   $243.05   $243.00  
  Purchase #3 $69.83   8.665%   $75.8808   $75.88   $75.90   $75.90  
  Purchase #4 $20.39   12.855%   $23.0111   $23.01   $23.00   $23.00  
  Purchase #5 $100.63   12.591%   $113.3003   $113.30   $113.30   $113.30  
  Purchase #6 $231.33   4.110%   $240.8377   $240.84   $240.85   $240.80  
  Purchase #7 $103.79   12.300%   $116.5562   $116.56   $116.55   $116.60  
  7 purchase totals = $777.10       $854.2064   $854.21   $854.25   $854.20