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 $131.85   11.191%   $146.6053   $146.61   $146.60   $146.60  
  Purchase #2 $174.94   6.556%   $186.4091   $186.41   $186.40   $186.40  
  Purchase #3 $240.99   13.192%   $272.7814   $272.78   $272.80   $272.80  
  Purchase #4 $239.65   7.614%   $257.897   $257.90   $257.90   $257.90  
  Purchase #5 $82.29   3.319%   $85.0212   $85.02   $85.00   $85.00  
  Purchase #6 $101.50   5.208%   $106.7861   $106.79   $106.80   $106.80  
  Purchase #7 $145.30   9.270%   $158.7693   $158.77   $158.75   $158.80  
  7 purchase totals = $1,116.52       $1,214.2694   $1,214.28   $1,214.25   $1,214.30