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 $67.78   10.527%   $74.9152   $74.92   $74.90   $74.90  
  Purchase #2 $208.77   7.166%   $223.7305   $223.73   $223.75   $223.70  
  Purchase #3 $137.72   12.727%   $155.2476   $155.25   $155.25   $155.20  
  Purchase #4 $81.89   11.450%   $91.2664   $91.27   $91.25   $91.30  
  Purchase #5 $203.46   4.122%   $211.8466   $211.85   $211.85   $211.80  
  Purchase #6 $223.50   13.242%   $253.0959   $253.10   $253.10   $253.10  
  Purchase #7 $32.29   5.844%   $34.177   $34.18   $34.20   $34.20  
  7 purchase totals = $955.41       $1,044.2792   $1,044.30   $1,044.30   $1,044.20