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 $65.47   4.104%   $68.1569   $68.16   $68.15   $68.20  
  Purchase #2 $222.76   7.621%   $239.7365   $239.74   $239.75   $239.70  
  Purchase #3 $176.68   8.446%   $191.6024   $191.60   $191.60   $191.60  
  Purchase #4 $246.68   3.366%   $254.9832   $254.98   $255.00   $255.00  
  Purchase #5 $108.51   13.751%   $123.4312   $123.43   $123.45   $123.40  
  Purchase #6 $177.57   13.449%   $201.4514   $201.45   $201.45   $201.50  
  Purchase #7 $250.87   7.604%   $269.9462   $269.95   $269.95   $269.90  
  7 purchase totals = $1,248.54       $1,349.3078   $1,349.31   $1,349.35   $1,349.30