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 $163.68   12.735%   $184.5246   $184.52   $184.50   $184.50  
  Purchase #2 $16.61   5.510%   $17.5252   $17.53   $17.55   $17.50  
  Purchase #3 $38.27   7.261%   $41.0488   $41.05   $41.05   $41.00  
  Purchase #4 $114.95   12.615%   $129.4509   $129.45   $129.45   $129.50  
  Purchase #5 $125.93   5.222%   $132.5061   $132.51   $132.50   $132.50  
  Purchase #6 $116.96   8.236%   $126.5928   $126.59   $126.60   $126.60  
  Purchase #7 $196.45   5.165%   $206.5966   $206.60   $206.60   $206.60  
  7 purchase totals = $772.85       $838.2450   $838.25   $838.25   $838.20