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 $113.61   3.123%   $117.158   $117.16   $117.15   $117.20  
  Purchase #2 $201.89   12.396%   $226.9163   $226.92   $226.90   $226.90  
  Purchase #3 $58.88   13.199%   $66.6516   $66.65   $66.65   $66.70  
  Purchase #4 $120.59   8.229%   $130.5134   $130.51   $130.50   $130.50  
  Purchase #5 $217.92   10.104%   $239.9386   $239.94   $239.95   $239.90  
  Purchase #6 $25.61   4.174%   $26.679   $26.68   $26.70   $26.70  
  Purchase #7 $35.83   8.403%   $38.8408   $38.84   $38.85   $38.80  
  7 purchase totals = $774.33       $846.6977   $846.70   $846.70   $846.70