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 $203.33   13.228%   $230.2265   $230.23   $230.25   $230.20  
  Purchase #2 $44.60   11.357%   $49.6652   $49.67   $49.65   $49.70  
  Purchase #3 $84.49   4.214%   $88.0504   $88.05   $88.05   $88.10  
  Purchase #4 $227.55   7.259%   $244.0679   $244.07   $244.05   $244.10  
  Purchase #5 $23.81   10.403%   $26.287   $26.29   $26.30   $26.30  
  Purchase #6 $79.26   7.178%   $84.9493   $84.95   $84.95   $84.90  
  Purchase #7 $232.49   8.385%   $251.9843   $251.98   $252.00   $252.00  
  7 purchase totals = $895.53       $975.2306   $975.24   $975.25   $975.30