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 $91.30   5.771%   $96.5689   $96.57   $96.55   $96.60  
  Purchase #2 $40.96   7.408%   $43.9943   $43.99   $44.00   $44.00  
  Purchase #3 $191.43   4.798%   $200.6148   $200.61   $200.60   $200.60  
  Purchase #4 $189.97   8.694%   $206.486   $206.49   $206.50   $206.50  
  Purchase #5 $159.52   3.275%   $164.7443   $164.74   $164.75   $164.70  
  Purchase #6 $231.90   10.862%   $257.089   $257.09   $257.10   $257.10  
  Purchase #7 $46.54   9.750%   $51.0777   $51.08   $51.10   $51.10  
  7 purchase totals = $951.62       $1,020.5750   $1,020.57   $1,020.60   $1,020.60