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 $61.84   11.401%   $68.8904   $68.89   $68.90   $68.90  
  Purchase #2 $46.96   12.487%   $52.8239   $52.82   $52.80   $52.80  
  Purchase #3 $102.69   4.653%   $107.4682   $107.47   $107.45   $107.50  
  Purchase #4 $25.77   9.306%   $28.1682   $28.17   $28.15   $28.20  
  Purchase #5 $102.64   10.651%   $113.5722   $113.57   $113.55   $113.60  
  Purchase #6 $33.79   5.771%   $35.74   $35.74   $35.75   $35.70  
  Purchase #7 $58.57   7.132%   $62.7472   $62.75   $62.75   $62.70  
  7 purchase totals = $432.26       $469.4101   $469.41   $469.35   $469.40