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 $225.74   4.827%   $236.6365   $236.64   $236.65   $236.60  
  Purchase #2 $175.91   10.630%   $194.6092   $194.61   $194.60   $194.60  
  Purchase #3 $143.33   10.155%   $157.8852   $157.89   $157.90   $157.90  
  Purchase #4 $66.72   8.129%   $72.1437   $72.14   $72.15   $72.10  
  Purchase #5 $137.77   5.515%   $145.368   $145.37   $145.35   $145.40  
  Purchase #6 $49.82   5.787%   $52.7031   $52.70   $52.70   $52.70  
  Purchase #7 $192.72   3.268%   $199.0181   $199.02   $199.00   $199.00  
  7 purchase totals = $992.01       $1,058.3638   $1,058.37   $1,058.35   $1,058.30