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 $246.93   11.567%   $275.4924   $275.49   $275.50   $275.50  
  Purchase #2 $230.79   3.705%   $239.3408   $239.34   $239.35   $239.30  
  Purchase #3 $243.95   7.395%   $261.9901   $261.99   $262.00   $262.00  
  Purchase #4 $42.98   3.567%   $44.5131   $44.51   $44.50   $44.50  
  Purchase #5 $250.74   9.144%   $273.6677   $273.67   $273.65   $273.70  
  Purchase #6 $22.72   10.561%   $25.1195   $25.12   $25.10   $25.10  
  Purchase #7 $31.27   11.249%   $34.7876   $34.79   $34.80   $34.80  
  7 purchase totals = $1,069.38       $1,154.9112   $1,154.91   $1,154.90   $1,154.90