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 $212.84   3.265%   $219.7892   $219.79   $219.80   $219.80  
  Purchase #2 $89.31   3.716%   $92.6288   $92.63   $92.65   $92.60  
  Purchase #3 $38.96   7.173%   $41.7546   $41.75   $41.75   $41.80  
  Purchase #4 $69.55   8.646%   $75.5633   $75.56   $75.55   $75.60  
  Purchase #5 $208.76   3.593%   $216.2607   $216.26   $216.25   $216.30  
  Purchase #6 $98.90   6.270%   $105.101   $105.10   $105.10   $105.10  
  Purchase #7 $237.56   10.199%   $261.7887   $261.79   $261.80   $261.80  
  7 purchase totals = $955.88       $1,012.8863   $1,012.88   $1,012.90   $1,013.00