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 $147.46   12.363%   $165.6905   $165.69   $165.70   $165.70  
  Purchase #2 $59.89   12.755%   $67.529   $67.53   $67.55   $67.50  
  Purchase #3 $183.81   13.127%   $207.9387   $207.94   $207.95   $207.90  
  Purchase #4 $143.33   4.280%   $149.4645   $149.46   $149.45   $149.50  
  Purchase #5 $5.90   7.293%   $6.3303   $6.33   $6.35   $6.30  
  Purchase #6 $49.98   3.829%   $51.8937   $51.89   $51.90   $51.90  
  Purchase #7 $207.92   12.161%   $233.2052   $233.21   $233.20   $233.20  
  7 purchase totals = $798.29       $882.0519   $882.05   $882.10   $882.00