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 $52.25   13.867%   $59.4955   $59.50   $59.50   $59.50  
  Purchase #2 $126.49   6.384%   $134.5651   $134.57   $134.55   $134.60  
  Purchase #3 $201.32   11.154%   $223.7752   $223.78   $223.80   $223.80  
  Purchase #4 $222.45   4.602%   $232.6871   $232.69   $232.70   $232.70  
  Purchase #5 $191.68   11.822%   $214.3404   $214.34   $214.35   $214.30  
  Purchase #6 $79.82   9.143%   $87.1179   $87.12   $87.10   $87.10  
  Purchase #7 $107.43   10.329%   $118.5264   $118.53   $118.55   $118.50  
  7 purchase totals = $981.44       $1,070.5076   $1,070.53   $1,070.55   $1,070.50