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 $215.47   7.588%   $231.8199   $231.82   $231.80   $231.80  
  Purchase #2 $243.78   9.293%   $266.4345   $266.43   $266.45   $266.40  
  Purchase #3 $181.55   13.212%   $205.5364   $205.54   $205.55   $205.50  
  Purchase #4 $164.54   4.843%   $172.5087   $172.51   $172.50   $172.50  
  Purchase #5 $198.71   12.715%   $223.976   $223.98   $224.00   $224.00  
  Purchase #6 $138.75   13.613%   $157.638   $157.64   $157.65   $157.60  
  Purchase #7 $22.79   7.255%   $24.4434   $24.44   $24.45   $24.40  
  7 purchase totals = $1,165.59       $1,282.3569   $1,282.36   $1,282.40   $1,282.20