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 $56.95   5.636%   $60.1597   $60.16   $60.15   $60.20  
  Purchase #2 $140.79   6.338%   $149.7133   $149.71   $149.70   $149.70  
  Purchase #3 $122.65   7.633%   $132.0119   $132.01   $132.00   $132.00  
  Purchase #4 $202.76   13.694%   $230.526   $230.53   $230.55   $230.50  
  Purchase #5 $157.49   7.120%   $168.7033   $168.70   $168.70   $168.70  
  Purchase #6 $202.50   7.350%   $217.3838   $217.38   $217.40   $217.40  
  Purchase #7 $85.91   7.177%   $92.0758   $92.08   $92.10   $92.10  
  7 purchase totals = $969.05       $1,050.5738   $1,050.57   $1,050.60   $1,050.60