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 $71.25   8.558%   $77.3476   $77.35   $77.35   $77.30  
  Purchase #2 $229.33   12.788%   $258.6567   $258.66   $258.65   $258.70  
  Purchase #3 $120.34   11.561%   $134.2525   $134.25   $134.25   $134.30  
  Purchase #4 $155.55   12.206%   $174.5364   $174.54   $174.55   $174.50  
  Purchase #5 $219.88   13.834%   $250.2982   $250.30   $250.30   $250.30  
  Purchase #6 $19.93   3.118%   $20.5514   $20.55   $20.55   $20.60  
  Purchase #7 $115.58   11.357%   $128.7064   $128.71   $128.70   $128.70  
  7 purchase totals = $931.86       $1,044.3492   $1,044.36   $1,044.35   $1,044.40