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 $112.70   7.644%   $121.3148   $121.31   $121.30   $121.30  
  Purchase #2 $77.30   3.423%   $79.946   $79.95   $79.95   $79.90  
  Purchase #3 $89.54   12.467%   $100.703   $100.70   $100.70   $100.70  
  Purchase #4 $45.37   3.212%   $46.8273   $46.83   $46.85   $46.80  
  Purchase #5 $147.86   9.338%   $161.6672   $161.67   $161.65   $161.70  
  Purchase #6 $191.79   5.576%   $202.4842   $202.48   $202.50   $202.50  
  Purchase #7 $169.38   3.349%   $175.0525   $175.05   $175.05   $175.10  
  7 purchase totals = $833.94       $887.9950   $887.99   $888.00   $888.00