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 $216.87   6.749%   $231.5066   $231.51   $231.50   $231.50  
  Purchase #2 $57.51   3.702%   $59.639   $59.64   $59.65   $59.60  
  Purchase #3 $58.58   12.329%   $65.8023   $65.80   $65.80   $65.80  
  Purchase #4 $182.34   6.704%   $194.5641   $194.56   $194.55   $194.60  
  Purchase #5 $141.34   3.252%   $145.9364   $145.94   $145.95   $145.90  
  Purchase #6 $116.66   6.304%   $124.0142   $124.01   $124.00   $124.00  
  Purchase #7 $129.65   8.463%   $140.6223   $140.62   $140.60   $140.60  
  7 purchase totals = $902.95       $962.0849   $962.08   $962.05   $962.00