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 $11.85   13.408%   $13.4388   $13.44   $13.45   $13.40  
  Purchase #2 $160.69   5.562%   $169.6276   $169.63   $169.65   $169.60  
  Purchase #3 $238.81   5.389%   $251.6795   $251.68   $251.70   $251.70  
  Purchase #4 $52.48   5.501%   $55.3669   $55.37   $55.35   $55.40  
  Purchase #5 $223.95   12.594%   $252.1543   $252.15   $252.15   $252.20  
  Purchase #6 $146.49   6.376%   $155.8302   $155.83   $155.85   $155.80  
  Purchase #7 $94.78   11.564%   $105.7404   $105.74   $105.75   $105.70  
  7 purchase totals = $929.05       $1,003.8377   $1,003.84   $1,003.90   $1,003.80