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 $64.70   6.774%   $69.0828   $69.08   $69.10   $69.10  
  Purchase #2 $75.65   11.863%   $84.6244   $84.62   $84.60   $84.60  
  Purchase #3 $119.96   6.555%   $127.8234   $127.82   $127.80   $127.80  
  Purchase #4 $87.86   13.468%   $99.693   $99.69   $99.70   $99.70  
  Purchase #5 $154.45   8.295%   $167.2616   $167.26   $167.25   $167.30  
  Purchase #6 $165.70   10.591%   $183.2493   $183.25   $183.25   $183.20  
  Purchase #7 $142.85   13.545%   $162.199   $162.20   $162.20   $162.20  
  7 purchase totals = $811.17       $893.9335   $893.92   $893.90   $893.90