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 $138.95   5.209%   $146.1879   $146.19   $146.20   $146.20  
  Purchase #2 $169.86   12.539%   $191.1587   $191.16   $191.15   $191.20  
  Purchase #3 $69.95   10.751%   $77.4703   $77.47   $77.45   $77.50  
  Purchase #4 $160.50   3.254%   $165.7227   $165.72   $165.70   $165.70  
  Purchase #5 $178.98   13.278%   $202.745   $202.75   $202.75   $202.70  
  Purchase #6 $217.81   10.724%   $241.1679   $241.17   $241.15   $241.20  
  Purchase #7 $89.36   6.829%   $95.4624   $95.46   $95.45   $95.50  
  7 purchase totals = $1,025.41       $1,119.9149   $1,119.92   $1,119.85   $1,120.00