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 $58.77   3.819%   $61.0144   $61.01   $61.00   $61.00  
  Purchase #2 $106.80   13.106%   $120.7972   $120.80   $120.80   $120.80  
  Purchase #3 $164.34   6.811%   $175.5332   $175.53   $175.55   $175.50  
  Purchase #4 $135.27   6.473%   $144.026   $144.03   $144.05   $144.00  
  Purchase #5 $210.30   4.147%   $219.0211   $219.02   $219.00   $219.00  
  Purchase #6 $250.37   8.414%   $271.4361   $271.44   $271.45   $271.40  
  Purchase #7 $211.47   4.851%   $221.7284   $221.73   $221.75   $221.70  
  7 purchase totals = $1,137.32       $1,213.5564   $1,213.56   $1,213.60   $1,213.40