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 $70.46   7.273%   $75.5846   $75.58   $75.60   $75.60  
  Purchase #2 $173.31   12.131%   $194.3342   $194.33   $194.35   $194.30  
  Purchase #3 $118.78   6.483%   $126.4805   $126.48   $126.50   $126.50  
  Purchase #4 $5.93   7.482%   $6.3737   $6.37   $6.35   $6.40  
  Purchase #5 $148.67   12.477%   $167.2196   $167.22   $167.20   $167.20  
  Purchase #6 $73.27   6.537%   $78.0597   $78.06   $78.05   $78.10  
  Purchase #7 $123.89   10.287%   $136.6346   $136.63   $136.65   $136.60  
  7 purchase totals = $714.31       $784.6869   $784.67   $784.70   $784.70