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 $131.35   7.236%   $140.8545   $140.85   $140.85   $140.90  
  Purchase #2 $122.67   5.257%   $129.1188   $129.12   $129.10   $129.10  
  Purchase #3 $44.94   6.650%   $47.9285   $47.93   $47.95   $47.90  
  Purchase #4 $143.91   3.481%   $148.9195   $148.92   $148.90   $148.90  
  Purchase #5 $137.60   11.352%   $153.2204   $153.22   $153.20   $153.20  
  Purchase #6 $147.39   8.194%   $159.4671   $159.47   $159.45   $159.50  
  Purchase #7 $122.46   9.535%   $134.1366   $134.14   $134.15   $134.10  
  7 purchase totals = $850.32       $913.6454   $913.65   $913.60   $913.60