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 $61.89   6.124%   $65.6801   $65.68   $65.70   $65.70  
  Purchase #2 $38.57   6.274%   $40.9899   $40.99   $41.00   $41.00  
  Purchase #3 $228.84   6.418%   $243.527   $243.53   $243.55   $243.50  
  Purchase #4 $222.49   4.169%   $231.7656   $231.77   $231.75   $231.80  
  Purchase #5 $64.43   6.416%   $68.5638   $68.56   $68.55   $68.60  
  Purchase #6 $177.50   6.132%   $188.3843   $188.38   $188.40   $188.40  
  Purchase #7 $157.72   13.260%   $178.6337   $178.63   $178.65   $178.60  
  7 purchase totals = $951.44       $1,017.5444   $1,017.54   $1,017.60   $1,017.60