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 $92.72   4.579%   $96.9656   $96.97   $96.95   $97.00  
  Purchase #2 $230.44   11.813%   $257.6619   $257.66   $257.65   $257.70  
  Purchase #3 $203.86   4.814%   $213.6738   $213.67   $213.65   $213.70  
  Purchase #4 $170.29   13.319%   $192.9709   $192.97   $192.95   $193.00  
  Purchase #5 $111.89   12.295%   $125.6469   $125.65   $125.65   $125.60  
  Purchase #6 $125.76   12.617%   $141.6271   $141.63   $141.65   $141.60  
  Purchase #7 $154.40   10.801%   $171.0767   $171.08   $171.10   $171.10  
  7 purchase totals = $1,089.36       $1,199.6229   $1,199.63   $1,199.60   $1,199.70