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 $207.86   8.376%   $225.2704   $225.27   $225.25   $225.30  
  Purchase #2 $221.67   6.758%   $236.6505   $236.65   $236.65   $236.70  
  Purchase #3 $28.60   12.797%   $32.2599   $32.26   $32.25   $32.30  
  Purchase #4 $147.82   5.653%   $156.1763   $156.18   $156.20   $156.20  
  Purchase #5 $11.31   3.709%   $11.7295   $11.73   $11.75   $11.70  
  Purchase #6 $49.90   7.627%   $53.7059   $53.71   $53.70   $53.70  
  Purchase #7 $181.69   13.442%   $206.1128   $206.11   $206.10   $206.10  
  7 purchase totals = $848.85       $921.9053   $921.91   $921.90   $922.00