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 $214.31   9.585%   $234.8516   $234.85   $234.85   $234.90  
  Purchase #2 $113.46   10.190%   $125.0216   $125.02   $125.00   $125.00  
  Purchase #3 $229.68   8.701%   $249.6645   $249.66   $249.65   $249.70  
  Purchase #4 $46.95   5.155%   $49.3703   $49.37   $49.35   $49.40  
  Purchase #5 $52.72   4.661%   $55.1773   $55.18   $55.20   $55.20  
  Purchase #6 $185.58   10.365%   $204.8154   $204.82   $204.80   $204.80  
  Purchase #7 $82.86   12.622%   $93.3186   $93.32   $93.30   $93.30  
  7 purchase totals = $925.56       $1,012.2193   $1,012.22   $1,012.15   $1,012.30