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 $237.88   10.409%   $262.6409   $262.64   $262.65   $262.60  
  Purchase #2 $152.68   8.291%   $165.3387   $165.34   $165.35   $165.30  
  Purchase #3 $60.95   3.459%   $63.0583   $63.06   $63.05   $63.10  
  Purchase #4 $134.85   12.826%   $152.1459   $152.15   $152.15   $152.10  
  Purchase #5 $8.77   10.310%   $9.6742   $9.67   $9.65   $9.70  
  Purchase #6 $155.39   13.132%   $175.7958   $175.80   $175.80   $175.80  
  Purchase #7 $204.31   9.600%   $223.9238   $223.92   $223.90   $223.90  
  7 purchase totals = $954.83       $1,052.5776   $1,052.58   $1,052.55   $1,052.50