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 $248.44   10.732%   $275.1026   $275.10   $275.10   $275.10  
  Purchase #2 $80.94   7.228%   $86.7903   $86.79   $86.80   $86.80  
  Purchase #3 $74.75   3.408%   $77.2975   $77.30   $77.30   $77.30  
  Purchase #4 $218.60   6.177%   $232.1029   $232.10   $232.10   $232.10  
  Purchase #5 $210.96   10.873%   $233.8977   $233.90   $233.90   $233.90  
  Purchase #6 $73.76   13.871%   $83.9912   $83.99   $84.00   $84.00  
  Purchase #7 $58.76   11.567%   $65.5568   $65.56   $65.55   $65.60  
  7 purchase totals = $966.21       $1,054.7390   $1,054.74   $1,054.75   $1,054.80