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 $95.64   9.837%   $105.0481   $105.05   $105.05   $105.00  
  Purchase #2 $165.99   13.653%   $188.6526   $188.65   $188.65   $188.70  
  Purchase #3 $226.37   3.164%   $233.5323   $233.53   $233.55   $233.50  
  Purchase #4 $36.69   8.663%   $39.8685   $39.87   $39.85   $39.90  
  Purchase #5 $228.55   11.867%   $255.672   $255.67   $255.65   $255.70  
  Purchase #6 $241.29   3.850%   $250.5797   $250.58   $250.60   $250.60  
  Purchase #7 $20.58   13.212%   $23.299   $23.30   $23.30   $23.30  
  7 purchase totals = $1,015.11       $1,096.6522   $1,096.65   $1,096.65   $1,096.70