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 $87.86   9.261%   $95.9967   $96.00   $96.00   $96.00  
  Purchase #2 $116.94   5.811%   $123.7354   $123.74   $123.75   $123.70  
  Purchase #3 $187.62   3.316%   $193.8415   $193.84   $193.85   $193.80  
  Purchase #4 $54.48   6.374%   $57.9526   $57.95   $57.95   $58.00  
  Purchase #5 $81.82   7.512%   $87.9663   $87.97   $87.95   $88.00  
  Purchase #6 $220.80   13.309%   $250.1863   $250.19   $250.20   $250.20  
  Purchase #7 $131.56   10.411%   $145.2567   $145.26   $145.25   $145.30  
  7 purchase totals = $881.08       $954.9355   $954.95   $954.95   $955.00