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 $48.33   3.515%   $50.0288   $50.03   $50.05   $50.00  
  Purchase #2 $115.58   8.261%   $125.1281   $125.13   $125.15   $125.10  
  Purchase #3 $5.95   3.709%   $6.1707   $6.17   $6.15   $6.20  
  Purchase #4 $23.32   5.472%   $24.5961   $24.60   $24.60   $24.60  
  Purchase #5 $148.90   4.320%   $155.3325   $155.33   $155.35   $155.30  
  Purchase #6 $243.56   6.847%   $260.2366   $260.24   $260.25   $260.20  
  Purchase #7 $219.66   8.590%   $238.5288   $238.53   $238.55   $238.50  
  7 purchase totals = $805.30       $860.0216   $860.03   $860.10   $859.90