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 $213.65   6.323%   $227.1591   $227.16   $227.15   $227.20  
  Purchase #2 $240.50   9.317%   $262.9074   $262.91   $262.90   $262.90  
  Purchase #3 $82.35   12.767%   $92.8636   $92.86   $92.85   $92.90  
  Purchase #4 $246.57   8.752%   $268.1498   $268.15   $268.15   $268.10  
  Purchase #5 $154.70   6.724%   $165.102   $165.10   $165.10   $165.10  
  Purchase #6 $112.98   8.850%   $122.9787   $122.98   $123.00   $123.00  
  Purchase #7 $212.97   11.288%   $237.0101   $237.01   $237.00   $237.00  
  7 purchase totals = $1,263.72       $1,376.1707   $1,376.17   $1,376.15   $1,376.20