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 $113.75   11.239%   $126.5344   $126.53   $126.55   $126.50  
  Purchase #2 $75.37   8.496%   $81.7734   $81.77   $81.75   $81.80  
  Purchase #3 $16.93   12.484%   $19.0435   $19.04   $19.05   $19.00  
  Purchase #4 $68.80   5.708%   $72.7271   $72.73   $72.75   $72.70  
  Purchase #5 $144.82   10.173%   $159.5525   $159.55   $159.55   $159.60  
  Purchase #6 $246.57   10.635%   $272.7927   $272.79   $272.80   $272.80  
  Purchase #7 $66.86   10.774%   $74.0635   $74.06   $74.05   $74.10  
  7 purchase totals = $733.10       $806.4871   $806.47   $806.50   $806.50