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 $91.66   7.489%   $98.5244   $98.52   $98.50   $98.50  
  Purchase #2 $228.43   6.198%   $242.5881   $242.59   $242.60   $242.60  
  Purchase #3 $196.83   3.509%   $203.7368   $203.74   $203.75   $203.70  
  Purchase #4 $62.66   3.565%   $64.8938   $64.89   $64.90   $64.90  
  Purchase #5 $173.47   6.751%   $185.181   $185.18   $185.20   $185.20  
  Purchase #6 $167.72   6.357%   $178.382   $178.38   $178.40   $178.40  
  Purchase #7 $208.57   10.273%   $229.9964   $230.00   $230.00   $230.00  
  7 purchase totals = $1,129.34       $1,203.3025   $1,203.30   $1,203.35   $1,203.30