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 $75.91   13.657%   $86.277   $86.28   $86.30   $86.30  
  Purchase #2 $66.70   11.805%   $74.5739   $74.57   $74.55   $74.60  
  Purchase #3 $220.58   8.657%   $239.6756   $239.68   $239.70   $239.70  
  Purchase #4 $95.89   12.228%   $107.6154   $107.62   $107.60   $107.60  
  Purchase #5 $193.89   11.385%   $215.9644   $215.96   $215.95   $216.00  
  Purchase #6 $228.68   5.415%   $241.063   $241.06   $241.05   $241.10  
  Purchase #7 $52.92   7.674%   $56.9811   $56.98   $57.00   $57.00  
  7 purchase totals = $934.57       $1,022.1504   $1,022.15   $1,022.15   $1,022.30