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 $63.52   11.379%   $70.7479   $70.75   $70.75   $70.70  
  Purchase #2 $93.47   4.115%   $97.3163   $97.32   $97.30   $97.30  
  Purchase #3 $241.45   6.749%   $257.7455   $257.75   $257.75   $257.70  
  Purchase #4 $239.30   4.649%   $250.4251   $250.43   $250.45   $250.40  
  Purchase #5 $33.44   3.576%   $34.6358   $34.64   $34.65   $34.60  
  Purchase #6 $225.63   5.793%   $238.7007   $238.70   $238.70   $238.70  
  Purchase #7 $57.89   9.501%   $63.3901   $63.39   $63.40   $63.40  
  7 purchase totals = $954.70       $1,012.9614   $1,012.98   $1,013.00   $1,012.80