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 $234.58   4.858%   $245.9759   $245.98   $246.00   $246.00  
  Purchase #2 $24.54   13.689%   $27.8993   $27.90   $27.90   $27.90  
  Purchase #3 $155.77   13.678%   $177.0762   $177.08   $177.10   $177.10  
  Purchase #4 $172.97   11.747%   $193.2888   $193.29   $193.30   $193.30  
  Purchase #5 $204.43   5.270%   $215.2035   $215.20   $215.20   $215.20  
  Purchase #6 $49.63   7.438%   $53.3215   $53.32   $53.30   $53.30  
  Purchase #7 $201.37   8.557%   $218.6012   $218.60   $218.60   $218.60  
  7 purchase totals = $1,043.29       $1,131.3664   $1,131.37   $1,131.40   $1,131.40