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 $108.85   9.643%   $119.3464   $119.35   $119.35   $119.30  
  Purchase #2 $246.94   7.848%   $266.3199   $266.32   $266.30   $266.30  
  Purchase #3 $168.65   10.503%   $186.3633   $186.36   $186.35   $186.40  
  Purchase #4 $82.38   6.600%   $87.8171   $87.82   $87.80   $87.80  
  Purchase #5 $247.25   11.248%   $275.0607   $275.06   $275.05   $275.10  
  Purchase #6 $177.38   4.553%   $185.4561   $185.46   $185.45   $185.50  
  Purchase #7 $142.82   4.519%   $149.274   $149.27   $149.25   $149.30  
  7 purchase totals = $1,174.27       $1,269.6375   $1,269.64   $1,269.55   $1,269.70