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 $130.79   12.201%   $146.7477   $146.75   $146.75   $146.70  
  Purchase #2 $206.82   13.468%   $234.6745   $234.67   $234.65   $234.70  
  Purchase #3 $193.34   3.692%   $200.4781   $200.48   $200.50   $200.50  
  Purchase #4 $142.91   5.743%   $151.1173   $151.12   $151.10   $151.10  
  Purchase #5 $228.98   9.439%   $250.5934   $250.59   $250.60   $250.60  
  Purchase #6 $242.87   10.408%   $268.1479   $268.15   $268.15   $268.10  
  Purchase #7 $86.37   5.667%   $91.2646   $91.26   $91.25   $91.30  
  7 purchase totals = $1,232.08       $1,343.0235   $1,343.02   $1,343.00   $1,343.00