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 $8.94   7.354%   $9.5974   $9.60   $9.60   $9.60  
  Purchase #2 $136.61   10.655%   $151.1658   $151.17   $151.15   $151.20  
  Purchase #3 $38.30   7.777%   $41.2786   $41.28   $41.30   $41.30  
  Purchase #4 $238.73   5.257%   $251.28   $251.28   $251.30   $251.30  
  Purchase #5 $126.57   11.720%   $141.404   $141.40   $141.40   $141.40  
  Purchase #6 $225.52   11.776%   $252.0772   $252.08   $252.10   $252.10  
  Purchase #7 $241.48   6.360%   $256.8381   $256.84   $256.85   $256.80  
  7 purchase totals = $1,016.15       $1,103.6411   $1,103.65   $1,103.70   $1,103.70