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 $123.61   8.566%   $134.1984   $134.20   $134.20   $134.20  
  Purchase #2 $171.71   7.168%   $184.0182   $184.02   $184.00   $184.00  
  Purchase #3 $203.68   7.170%   $218.2839   $218.28   $218.30   $218.30  
  Purchase #4 $246.82   8.274%   $267.2419   $267.24   $267.25   $267.20  
  Purchase #5 $10.92   6.237%   $11.6011   $11.60   $11.60   $11.60  
  Purchase #6 $155.48   6.373%   $165.3887   $165.39   $165.40   $165.40  
  Purchase #7 $187.53   5.557%   $197.951   $197.95   $197.95   $198.00  
  7 purchase totals = $1,099.75       $1,178.6832   $1,178.68   $1,178.70   $1,178.70