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 $244.93   7.647%   $263.6598   $263.66   $263.65   $263.70  
  Purchase #2 $88.34   10.617%   $97.7191   $97.72   $97.70   $97.70  
  Purchase #3 $19.95   3.497%   $20.6477   $20.65   $20.65   $20.60  
  Purchase #4 $49.97   6.851%   $53.3934   $53.39   $53.40   $53.40  
  Purchase #5 $91.80   9.323%   $100.3585   $100.36   $100.35   $100.40  
  Purchase #6 $246.33   7.627%   $265.1176   $265.12   $265.10   $265.10  
  Purchase #7 $200.32   10.569%   $221.4918   $221.49   $221.50   $221.50  
  7 purchase totals = $941.64       $1,022.3879   $1,022.39   $1,022.35   $1,022.40