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 $168.51   8.124%   $182.1998   $182.20   $182.20   $182.20  
  Purchase #2 $173.65   7.593%   $186.8352   $186.84   $186.85   $186.80  
  Purchase #3 $208.86   4.182%   $217.5945   $217.59   $217.60   $217.60  
  Purchase #4 $161.62   3.742%   $167.6678   $167.67   $167.65   $167.70  
  Purchase #5 $138.90   6.385%   $147.7688   $147.77   $147.75   $147.80  
  Purchase #6 $61.34   11.447%   $68.3616   $68.36   $68.35   $68.40  
  Purchase #7 $9.60   6.481%   $10.2222   $10.22   $10.20   $10.20  
  7 purchase totals = $922.48       $980.6499   $980.65   $980.60   $980.70