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 $248.91   13.606%   $282.7767   $282.78   $282.80   $282.80  
  Purchase #2 $182.31   10.580%   $201.5984   $201.60   $201.60   $201.60  
  Purchase #3 $181.71   5.637%   $191.953   $191.95   $191.95   $192.00  
  Purchase #4 $195.33   9.349%   $213.5914   $213.59   $213.60   $213.60  
  Purchase #5 $40.97   7.487%   $44.0374   $44.04   $44.05   $44.00  
  Purchase #6 $83.88   7.854%   $90.4679   $90.47   $90.45   $90.50  
  Purchase #7 $220.36   3.468%   $228.0021   $228.00   $228.00   $228.00  
  7 purchase totals = $1,153.47       $1,252.4269   $1,252.43   $1,252.45   $1,252.50