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 $134.89   7.838%   $145.4627   $145.46   $145.45   $145.50  
  Purchase #2 $157.86   11.299%   $175.6966   $175.70   $175.70   $175.70  
  Purchase #3 $62.25   11.411%   $69.3533   $69.35   $69.35   $69.40  
  Purchase #4 $249.84   7.620%   $268.8778   $268.88   $268.90   $268.90  
  Purchase #5 $53.95   5.545%   $56.9415   $56.94   $56.95   $56.90  
  Purchase #6 $126.95   7.136%   $136.0092   $136.01   $136.00   $136.00  
  Purchase #7 $72.44   5.692%   $76.5633   $76.56   $76.55   $76.60  
  7 purchase totals = $858.18       $928.9044   $928.90   $928.90   $929.00