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 $213.67   4.503%   $223.2916   $223.29   $223.30   $223.30  
  Purchase #2 $61.96   10.842%   $68.6777   $68.68   $68.70   $68.70  
  Purchase #3 $10.77   12.108%   $12.074   $12.07   $12.05   $12.10  
  Purchase #4 $246.67   11.407%   $274.8076   $274.81   $274.80   $274.80  
  Purchase #5 $241.25   9.208%   $263.4643   $263.46   $263.45   $263.50  
  Purchase #6 $116.65   11.650%   $130.2397   $130.24   $130.25   $130.20  
  Purchase #7 $72.34   6.746%   $77.2201   $77.22   $77.20   $77.20  
  7 purchase totals = $963.31       $1,049.7750   $1,049.77   $1,049.75   $1,049.80