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 $239.39   4.868%   $251.0435   $251.04   $251.05   $251.00  
  Purchase #2 $13.94   11.540%   $15.5487   $15.55   $15.55   $15.50  
  Purchase #3 $202.48   10.608%   $223.9591   $223.96   $223.95   $224.00  
  Purchase #4 $155.72   6.426%   $165.7266   $165.73   $165.75   $165.70  
  Purchase #5 $108.62   11.529%   $121.1428   $121.14   $121.15   $121.10  
  Purchase #6 $202.57   6.341%   $215.415   $215.42   $215.40   $215.40  
  Purchase #7 $50.25   3.478%   $51.9977   $52.00   $52.00   $52.00  
  7 purchase totals = $972.97       $1,044.8334   $1,044.84   $1,044.85   $1,044.70