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 $184.27   11.286%   $205.0667   $205.07   $205.05   $205.10  
  Purchase #2 $87.88   13.626%   $99.8545   $99.85   $99.85   $99.90  
  Purchase #3 $181.25   6.154%   $192.4041   $192.40   $192.40   $192.40  
  Purchase #4 $10.76   11.281%   $11.9738   $11.97   $11.95   $12.00  
  Purchase #5 $212.36   11.618%   $237.032   $237.03   $237.05   $237.00  
  Purchase #6 $52.41   10.780%   $58.0598   $58.06   $58.05   $58.10  
  Purchase #7 $154.69   10.618%   $171.115   $171.12   $171.10   $171.10  
  7 purchase totals = $883.62       $975.5059   $975.50   $975.45   $975.60