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 $249.43   7.751%   $268.7633   $268.76   $268.75   $268.80  
  Purchase #2 $167.59   4.260%   $174.7293   $174.73   $174.75   $174.70  
  Purchase #3 $125.37   7.396%   $134.6424   $134.64   $134.65   $134.60  
  Purchase #4 $99.51   7.784%   $107.2559   $107.26   $107.25   $107.30  
  Purchase #5 $136.36   6.349%   $145.0175   $145.02   $145.00   $145.00  
  Purchase #6 $84.35   10.265%   $93.0085   $93.01   $93.00   $93.00  
  Purchase #7 $23.82   9.142%   $25.9976   $26.00   $26.00   $26.00  
  7 purchase totals = $886.43       $949.4145   $949.42   $949.40   $949.40