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 $128.59   10.545%   $142.1498   $142.15   $142.15   $142.10  
  Purchase #2 $92.40   10.619%   $102.212   $102.21   $102.20   $102.20  
  Purchase #3 $224.36   5.200%   $236.0267   $236.03   $236.05   $236.00  
  Purchase #4 $139.64   4.434%   $145.8316   $145.83   $145.85   $145.80  
  Purchase #5 $33.39   10.855%   $37.0145   $37.01   $37.00   $37.00  
  Purchase #6 $178.48   3.435%   $184.6108   $184.61   $184.60   $184.60  
  Purchase #7 $7.42   13.708%   $8.4371   $8.44   $8.45   $8.40  
  7 purchase totals = $804.28       $856.2825   $856.28   $856.30   $856.10