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 $34.71   6.523%   $36.9741   $36.97   $36.95   $37.00  
  Purchase #2 $24.97   6.830%   $26.6755   $26.68   $26.70   $26.70  
  Purchase #3 $192.68   8.462%   $208.9846   $208.98   $209.00   $209.00  
  Purchase #4 $191.33   9.140%   $208.8176   $208.82   $208.80   $208.80  
  Purchase #5 $120.29   3.556%   $124.5675   $124.57   $124.55   $124.60  
  Purchase #6 $168.86   5.215%   $177.666   $177.67   $177.65   $177.70  
  Purchase #7 $167.68   5.330%   $176.6173   $176.62   $176.60   $176.60  
  7 purchase totals = $900.52       $960.3026   $960.31   $960.25   $960.40