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 $154.39   13.453%   $175.1601   $175.16   $175.15   $175.20  
  Purchase #2 $232.82   11.309%   $259.1496   $259.15   $259.15   $259.10  
  Purchase #3 $177.78   11.150%   $197.6025   $197.60   $197.60   $197.60  
  Purchase #4 $160.53   11.265%   $178.6137   $178.61   $178.60   $178.60  
  Purchase #5 $177.62   4.669%   $185.9131   $185.91   $185.90   $185.90  
  Purchase #6 $126.95   9.242%   $138.6827   $138.68   $138.70   $138.70  
  Purchase #7 $15.90   9.817%   $17.4609   $17.46   $17.45   $17.50  
  7 purchase totals = $1,045.99       $1,152.5826   $1,152.57   $1,152.55   $1,152.60