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 $232.98   8.151%   $251.9702   $251.97   $251.95   $252.00  
  Purchase #2 $55.98   13.360%   $63.4589   $63.46   $63.45   $63.50  
  Purchase #3 $232.82   4.214%   $242.631   $242.63   $242.65   $242.60  
  Purchase #4 $126.74   7.700%   $136.499   $136.50   $136.50   $136.50  
  Purchase #5 $234.58   4.854%   $245.9665   $245.97   $245.95   $246.00  
  Purchase #6 $145.55   3.741%   $150.995   $151.00   $151.00   $151.00  
  Purchase #7 $208.61   12.234%   $234.1313   $234.13   $234.15   $234.10  
  7 purchase totals = $1,237.26       $1,325.6519   $1,325.66   $1,325.65   $1,325.70