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 $121.28   4.637%   $126.9038   $126.90   $126.90   $126.90  
  Purchase #2 $58.94   9.483%   $64.5293   $64.53   $64.55   $64.50  
  Purchase #3 $195.82   4.253%   $204.1482   $204.15   $204.15   $204.10  
  Purchase #4 $216.44   5.169%   $227.6278   $227.63   $227.65   $227.60  
  Purchase #5 $126.89   11.502%   $141.4849   $141.48   $141.50   $141.50  
  Purchase #6 $153.59   13.527%   $174.3661   $174.37   $174.35   $174.40  
  Purchase #7 $101.84   11.121%   $113.1656   $113.17   $113.15   $113.20  
  7 purchase totals = $974.80       $1,052.2257   $1,052.23   $1,052.25   $1,052.20