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 $171.84   8.787%   $186.9396   $186.94   $186.95   $186.90  
  Purchase #2 $192.43   4.632%   $201.3434   $201.34   $201.35   $201.30  
  Purchase #3 $5.86   4.761%   $6.139   $6.14   $6.15   $6.10  
  Purchase #4 $223.79   9.745%   $245.5983   $245.60   $245.60   $245.60  
  Purchase #5 $115.28   11.807%   $128.8911   $128.89   $128.90   $128.90  
  Purchase #6 $61.71   5.351%   $65.0121   $65.01   $65.00   $65.00  
  Purchase #7 $177.81   11.660%   $198.5426   $198.54   $198.55   $198.50  
  7 purchase totals = $948.72       $1,032.4661   $1,032.46   $1,032.50   $1,032.30