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 $5.46   7.228%   $5.8546   $5.85   $5.85   $5.90  
  Purchase #2 $205.69   11.821%   $230.0046   $230.00   $230.00   $230.00  
  Purchase #3 $69.63   9.596%   $76.3117   $76.31   $76.30   $76.30  
  Purchase #4 $150.56   10.555%   $166.4516   $166.45   $166.45   $166.50  
  Purchase #5 $245.78   12.620%   $276.7974   $276.80   $276.80   $276.80  
  Purchase #6 $33.86   7.548%   $36.4158   $36.42   $36.40   $36.40  
  Purchase #7 $151.61   3.283%   $156.5874   $156.59   $156.60   $156.60  
  7 purchase totals = $862.59       $948.4231   $948.42   $948.40   $948.50