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 $63.46   9.777%   $69.6645   $69.66   $69.65   $69.70  
  Purchase #2 $149.66   12.524%   $168.4034   $168.40   $168.40   $168.40  
  Purchase #3 $8.53   10.845%   $9.4551   $9.46   $9.45   $9.50  
  Purchase #4 $119.88   5.757%   $126.7815   $126.78   $126.80   $126.80  
  Purchase #5 $218.74   11.259%   $243.3679   $243.37   $243.35   $243.40  
  Purchase #6 $208.46   3.621%   $216.0083   $216.01   $216.00   $216.00  
  Purchase #7 $220.55   3.772%   $228.8691   $228.87   $228.85   $228.90  
  7 purchase totals = $989.28       $1,062.5498   $1,062.55   $1,062.50   $1,062.70