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 $152.32   12.859%   $171.9068   $171.91   $171.90   $171.90  
  Purchase #2 $211.98   8.346%   $229.6719   $229.67   $229.65   $229.70  
  Purchase #3 $65.83   12.488%   $74.0509   $74.05   $74.05   $74.10  
  Purchase #4 $68.88   8.499%   $74.7341   $74.73   $74.75   $74.70  
  Purchase #5 $106.72   13.637%   $121.2734   $121.27   $121.25   $121.30  
  Purchase #6 $220.96   8.384%   $239.4853   $239.49   $239.50   $239.50  
  Purchase #7 $233.67   10.369%   $257.8992   $257.90   $257.90   $257.90  
  7 purchase totals = $1,060.36       $1,169.0216   $1,169.02   $1,169.00   $1,169.10