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 $84.79   8.847%   $92.2914   $92.29   $92.30   $92.30  
  Purchase #2 $218.36   4.266%   $227.6752   $227.68   $227.70   $227.70  
  Purchase #3 $88.29   9.783%   $96.9274   $96.93   $96.95   $96.90  
  Purchase #4 $154.30   6.229%   $163.9113   $163.91   $163.90   $163.90  
  Purchase #5 $77.70   4.808%   $81.4358   $81.44   $81.45   $81.40  
  Purchase #6 $105.50   5.113%   $110.8942   $110.89   $110.90   $110.90  
  Purchase #7 $198.26   10.631%   $219.337   $219.34   $219.35   $219.30  
  7 purchase totals = $927.20       $992.4723   $992.48   $992.55   $992.40