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 $248.98   10.693%   $275.6034   $275.60   $275.60   $275.60  
  Purchase #2 $149.59   10.460%   $165.2371   $165.24   $165.25   $165.20  
  Purchase #3 $71.81   9.539%   $78.66   $78.66   $78.65   $78.70  
  Purchase #4 $173.31   8.293%   $187.6826   $187.68   $187.70   $187.70  
  Purchase #5 $24.99   9.334%   $27.3226   $27.32   $27.30   $27.30  
  Purchase #6 $192.78   7.665%   $207.5566   $207.56   $207.55   $207.60  
  Purchase #7 $67.50   12.531%   $75.9584   $75.96   $75.95   $76.00  
  7 purchase totals = $928.96       $1,018.0207   $1,018.02   $1,018.00   $1,018.10