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 $33.51   10.421%   $37.0021   $37.00   $37.00   $37.00  
  Purchase #2 $84.67   11.602%   $94.4934   $94.49   $94.50   $94.50  
  Purchase #3 $230.39   3.624%   $238.7393   $238.74   $238.75   $238.70  
  Purchase #4 $116.60   12.247%   $130.88   $130.88   $130.90   $130.90  
  Purchase #5 $59.58   6.572%   $63.4956   $63.50   $63.50   $63.50  
  Purchase #6 $204.40   5.666%   $215.9813   $215.98   $216.00   $216.00  
  Purchase #7 $221.91   9.568%   $243.1423   $243.14   $243.15   $243.10  
  7 purchase totals = $951.06       $1,023.7340   $1,023.73   $1,023.80   $1,023.70