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 $245.69   9.487%   $268.9986   $269.00   $269.00   $269.00  
  Purchase #2 $178.38   13.596%   $202.6325   $202.63   $202.65   $202.60  
  Purchase #3 $83.25   5.219%   $87.5948   $87.59   $87.60   $87.60  
  Purchase #4 $13.86   4.168%   $14.4377   $14.44   $14.45   $14.40  
  Purchase #5 $100.98   5.483%   $106.5167   $106.52   $106.50   $106.50  
  Purchase #6 $165.75   8.629%   $180.0526   $180.05   $180.05   $180.10  
  Purchase #7 $245.39   7.231%   $263.1342   $263.13   $263.15   $263.10  
  7 purchase totals = $1,033.30       $1,123.3671   $1,123.36   $1,123.40   $1,123.30