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 $62.35   9.589%   $68.3287   $68.33   $68.35   $68.30  
  Purchase #2 $150.79   8.733%   $163.9585   $163.96   $163.95   $164.00  
  Purchase #3 $42.28   13.351%   $47.9248   $47.92   $47.90   $47.90  
  Purchase #4 $201.84   3.306%   $208.5128   $208.51   $208.50   $208.50  
  Purchase #5 $72.60   12.847%   $81.9269   $81.93   $81.95   $81.90  
  Purchase #6 $221.60   6.412%   $235.809   $235.81   $235.80   $235.80  
  Purchase #7 $227.92   6.375%   $242.4499   $242.45   $242.45   $242.40  
  7 purchase totals = $979.38       $1,048.9106   $1,048.91   $1,048.90   $1,048.80