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 $108.56   6.815%   $115.9584   $115.96   $115.95   $116.00  
  Purchase #2 $151.43   10.465%   $167.2771   $167.28   $167.30   $167.30  
  Purchase #3 $169.64   9.305%   $185.425   $185.43   $185.45   $185.40  
  Purchase #4 $250.94   9.574%   $274.965   $274.97   $274.95   $275.00  
  Purchase #5 $116.92   5.201%   $123.001   $123.00   $123.00   $123.00  
  Purchase #6 $103.83   4.364%   $108.3611   $108.36   $108.35   $108.40  
  Purchase #7 $50.83   3.638%   $52.6792   $52.68   $52.70   $52.70  
  7 purchase totals = $952.15       $1,027.6668   $1,027.68   $1,027.70   $1,027.80