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 $114.44   10.381%   $126.32   $126.32   $126.30   $126.30  
  Purchase #2 $62.32   10.389%   $68.7944   $68.79   $68.80   $68.80  
  Purchase #3 $52.93   10.244%   $58.3521   $58.35   $58.35   $58.40  
  Purchase #4 $227.70   9.793%   $249.9987   $250.00   $250.00   $250.00  
  Purchase #5 $192.98   12.631%   $217.3553   $217.36   $217.35   $217.40  
  Purchase #6 $66.58   12.354%   $74.8053   $74.81   $74.80   $74.80  
  Purchase #7 $191.63   10.396%   $211.5519   $211.55   $211.55   $211.60  
  7 purchase totals = $908.58       $1,007.1777   $1,007.18   $1,007.15   $1,007.30