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 $59.59   10.717%   $65.9763   $65.98   $66.00   $66.00  
  Purchase #2 $178.41   6.592%   $190.1708   $190.17   $190.15   $190.20  
  Purchase #3 $175.70   4.550%   $183.6944   $183.69   $183.70   $183.70  
  Purchase #4 $178.34   13.517%   $202.4462   $202.45   $202.45   $202.40  
  Purchase #5 $71.56   9.191%   $78.1371   $78.14   $78.15   $78.10  
  Purchase #6 $211.95   13.129%   $239.7769   $239.78   $239.80   $239.80  
  Purchase #7 $130.45   4.109%   $135.8102   $135.81   $135.80   $135.80  
  7 purchase totals = $1,006.00       $1,096.0119   $1,096.02   $1,096.05   $1,096.00