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 $44.82   9.782%   $49.2043   $49.20   $49.20   $49.20  
  Purchase #2 $220.83   8.229%   $239.0021   $239.00   $239.00   $239.00  
  Purchase #3 $148.41   4.577%   $155.2027   $155.20   $155.20   $155.20  
  Purchase #4 $222.27   5.269%   $233.9814   $233.98   $234.00   $234.00  
  Purchase #5 $181.56   9.714%   $199.1967   $199.20   $199.20   $199.20  
  Purchase #6 $190.65   11.728%   $213.0094   $213.01   $213.00   $213.00  
  Purchase #7 $74.59   5.432%   $78.6417   $78.64   $78.65   $78.60  
  7 purchase totals = $1,083.13       $1,168.2383   $1,168.23   $1,168.25   $1,168.20