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 $42.33   11.251%   $47.0925   $47.09   $47.10   $47.10  
  Purchase #2 $33.53   5.722%   $35.4486   $35.45   $35.45   $35.40  
  Purchase #3 $219.86   4.301%   $229.3162   $229.32   $229.30   $229.30  
  Purchase #4 $155.98   13.758%   $177.4397   $177.44   $177.45   $177.40  
  Purchase #5 $146.35   11.356%   $162.9695   $162.97   $162.95   $163.00  
  Purchase #6 $44.70   5.280%   $47.0602   $47.06   $47.05   $47.10  
  Purchase #7 $59.46   13.517%   $67.4972   $67.50   $67.50   $67.50  
  7 purchase totals = $702.21       $766.8239   $766.83   $766.80   $766.80