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 $249.67   10.841%   $276.7367   $276.74   $276.75   $276.70  
  Purchase #2 $88.39   5.505%   $93.2559   $93.26   $93.25   $93.30  
  Purchase #3 $26.67   12.165%   $29.9144   $29.91   $29.90   $29.90  
  Purchase #4 $110.89   6.547%   $118.15   $118.15   $118.15   $118.20  
  Purchase #5 $115.50   9.123%   $126.0371   $126.04   $126.05   $126.00  
  Purchase #6 $172.81   11.650%   $192.9424   $192.94   $192.95   $192.90  
  Purchase #7 $170.96   9.700%   $187.5431   $187.54   $187.55   $187.50  
  7 purchase totals = $934.89       $1,024.5796   $1,024.58   $1,024.60   $1,024.50