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 $204.95   6.505%   $218.282   $218.28   $218.30   $218.30  
  Purchase #2 $180.27   6.696%   $192.3409   $192.34   $192.35   $192.30  
  Purchase #3 $92.48   8.617%   $100.449   $100.45   $100.45   $100.40  
  Purchase #4 $230.99   5.182%   $242.9599   $242.96   $242.95   $243.00  
  Purchase #5 $248.62   6.395%   $264.5192   $264.52   $264.50   $264.50  
  Purchase #6 $35.82   6.283%   $38.0706   $38.07   $38.05   $38.10  
  Purchase #7 $67.61   3.872%   $70.2279   $70.23   $70.25   $70.20  
  7 purchase totals = $1,060.74       $1,126.8495   $1,126.85   $1,126.85   $1,126.80