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 $10.41   11.632%   $11.6209   $11.62   $11.60   $11.60  
  Purchase #2 $152.57   7.363%   $163.8037   $163.80   $163.80   $163.80  
  Purchase #3 $176.71   7.827%   $190.5411   $190.54   $190.55   $190.50  
  Purchase #4 $24.59   3.514%   $25.4541   $25.45   $25.45   $25.50  
  Purchase #5 $90.91   6.179%   $96.5273   $96.53   $96.55   $96.50  
  Purchase #6 $194.34   5.353%   $204.743   $204.74   $204.75   $204.70  
  Purchase #7 $161.84   12.306%   $181.756   $181.76   $181.75   $181.80  
  7 purchase totals = $811.37       $874.4461   $874.44   $874.45   $874.40