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 $124.39   8.501%   $134.9644   $134.96   $134.95   $135.00  
  Purchase #2 $237.77   3.482%   $246.0492   $246.05   $246.05   $246.00  
  Purchase #3 $86.38   12.633%   $97.2924   $97.29   $97.30   $97.30  
  Purchase #4 $110.61   5.169%   $116.3274   $116.33   $116.35   $116.30  
  Purchase #5 $200.28   3.766%   $207.8225   $207.82   $207.80   $207.80  
  Purchase #6 $212.89   6.480%   $226.6853   $226.69   $226.70   $226.70  
  Purchase #7 $44.86   5.675%   $47.4058   $47.41   $47.40   $47.40  
  7 purchase totals = $1,017.18       $1,076.5470   $1,076.55   $1,076.55   $1,076.50