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 $171.75   13.731%   $195.333   $195.33   $195.35   $195.30  
  Purchase #2 $217.98   4.533%   $227.861   $227.86   $227.85   $227.90  
  Purchase #3 $55.40   11.542%   $61.7943   $61.79   $61.80   $61.80  
  Purchase #4 $218.85   11.478%   $243.9696   $243.97   $243.95   $244.00  
  Purchase #5 $20.49   9.726%   $22.4829   $22.48   $22.50   $22.50  
  Purchase #6 $140.25   7.845%   $151.2526   $151.25   $151.25   $151.30  
  Purchase #7 $23.95   11.235%   $26.6408   $26.64   $26.65   $26.60  
  7 purchase totals = $848.67       $929.3342   $929.32   $929.35   $929.40