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 $243.87   13.280%   $276.2559   $276.26   $276.25   $276.30  
  Purchase #2 $142.54   9.247%   $155.7207   $155.72   $155.70   $155.70  
  Purchase #3 $118.76   11.578%   $132.51   $132.51   $132.50   $132.50  
  Purchase #4 $43.69   6.570%   $46.5604   $46.56   $46.55   $46.60  
  Purchase #5 $123.86   5.388%   $130.5336   $130.53   $130.55   $130.50  
  Purchase #6 $241.57   10.790%   $267.6354   $267.64   $267.65   $267.60  
  Purchase #7 $157.26   5.664%   $166.1672   $166.17   $166.15   $166.20  
  7 purchase totals = $1,071.55       $1,175.3832   $1,175.39   $1,175.35   $1,175.40