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 $216.41   13.559%   $245.753   $245.75   $245.75   $245.80  
  Purchase #2 $46.90   5.229%   $49.3524   $49.35   $49.35   $49.40  
  Purchase #3 $149.93   3.764%   $155.5734   $155.57   $155.55   $155.60  
  Purchase #4 $249.95   4.298%   $260.6929   $260.69   $260.70   $260.70  
  Purchase #5 $170.30   5.424%   $179.5371   $179.54   $179.55   $179.50  
  Purchase #6 $180.46   6.628%   $192.4209   $192.42   $192.40   $192.40  
  Purchase #7 $27.66   5.655%   $29.2242   $29.22   $29.20   $29.20  
  7 purchase totals = $1,041.61       $1,112.5539   $1,112.54   $1,112.50   $1,112.60