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 $76.94   11.577%   $85.8473   $85.85   $85.85   $85.80  
  Purchase #2 $207.75   4.375%   $216.8391   $216.84   $216.85   $216.80  
  Purchase #3 $12.32   4.217%   $12.8395   $12.84   $12.85   $12.80  
  Purchase #4 $146.46   10.612%   $162.0023   $162.00   $162.00   $162.00  
  Purchase #5 $41.37   4.136%   $43.0811   $43.08   $43.10   $43.10  
  Purchase #6 $160.98   9.802%   $176.7593   $176.76   $176.75   $176.80  
  Purchase #7 $133.97   12.699%   $150.9829   $150.98   $151.00   $151.00  
  7 purchase totals = $779.79       $848.3515   $848.35   $848.40   $848.30