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 $59.37   7.758%   $63.9759   $63.98   $64.00   $64.00  
  Purchase #2 $183.62   9.241%   $200.5883   $200.59   $200.60   $200.60  
  Purchase #3 $162.85   8.673%   $176.974   $176.97   $176.95   $177.00  
  Purchase #4 $79.83   6.194%   $84.7747   $84.77   $84.75   $84.80  
  Purchase #5 $80.98   9.450%   $88.6326   $88.63   $88.65   $88.60  
  Purchase #6 $76.85   9.616%   $84.2399   $84.24   $84.25   $84.20  
  Purchase #7 $167.51   8.601%   $181.9175   $181.92   $181.90   $181.90  
  7 purchase totals = $811.01       $881.1029   $881.10   $881.10   $881.10