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 $205.29   11.470%   $228.8368   $228.84   $228.85   $228.80  
  Purchase #2 $236.70   12.759%   $266.9006   $266.90   $266.90   $266.90  
  Purchase #3 $21.66   13.419%   $24.5666   $24.57   $24.55   $24.60  
  Purchase #4 $38.65   9.593%   $42.3577   $42.36   $42.35   $42.40  
  Purchase #5 $30.90   3.697%   $32.0424   $32.04   $32.05   $32.00  
  Purchase #6 $225.57   7.135%   $241.6644   $241.66   $241.65   $241.70  
  Purchase #7 $176.89   7.427%   $190.0276   $190.03   $190.05   $190.00  
  7 purchase totals = $935.66       $1,026.3961   $1,026.40   $1,026.40   $1,026.40