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 $58.81   4.173%   $61.2641   $61.26   $61.25   $61.30  
  Purchase #2 $181.34   12.182%   $203.4308   $203.43   $203.45   $203.40  
  Purchase #3 $73.93   13.479%   $83.895   $83.90   $83.90   $83.90  
  Purchase #4 $153.30   7.673%   $165.0627   $165.06   $165.05   $165.10  
  Purchase #5 $210.41   4.235%   $219.3209   $219.32   $219.30   $219.30  
  Purchase #6 $88.40   5.114%   $92.9208   $92.92   $92.90   $92.90  
  Purchase #7 $28.30   4.412%   $29.5486   $29.55   $29.55   $29.50  
  7 purchase totals = $794.49       $855.4429   $855.44   $855.40   $855.40