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 $157.46   11.747%   $175.9568   $175.96   $175.95   $176.00  
  Purchase #2 $61.89   12.566%   $69.6671   $69.67   $69.65   $69.70  
  Purchase #3 $103.55   6.553%   $110.3356   $110.34   $110.35   $110.30  
  Purchase #4 $33.86   7.364%   $36.3535   $36.35   $36.35   $36.40  
  Purchase #5 $189.61   10.867%   $210.2149   $210.21   $210.20   $210.20  
  Purchase #6 $235.79   5.819%   $249.5106   $249.51   $249.50   $249.50  
  Purchase #7 $216.94   11.103%   $241.0268   $241.03   $241.05   $241.00  
  7 purchase totals = $999.10       $1,093.0653   $1,093.07   $1,093.05   $1,093.10