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 $207.37   11.396%   $231.0019   $231.00   $231.00   $231.00  
  Purchase #2 $155.87   3.140%   $160.7643   $160.76   $160.75   $160.80  
  Purchase #3 $148.50   5.383%   $156.4938   $156.49   $156.50   $156.50  
  Purchase #4 $195.81   12.635%   $220.5506   $220.55   $220.55   $220.60  
  Purchase #5 $13.52   3.395%   $13.979   $13.98   $14.00   $14.00  
  Purchase #6 $35.92   5.539%   $37.9096   $37.91   $37.90   $37.90  
  Purchase #7 $234.77   3.357%   $242.6512   $242.65   $242.65   $242.70  
  7 purchase totals = $991.76       $1,063.3504   $1,063.34   $1,063.35   $1,063.50