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 $57.53   10.485%   $63.562   $63.56   $63.55   $63.60  
  Purchase #2 $136.64   5.414%   $144.0377   $144.04   $144.05   $144.00  
  Purchase #3 $179.82   4.222%   $187.412   $187.41   $187.40   $187.40  
  Purchase #4 $109.95   4.278%   $114.6537   $114.65   $114.65   $114.70  
  Purchase #5 $241.92   5.668%   $255.632   $255.63   $255.65   $255.60  
  Purchase #6 $53.35   3.688%   $55.3175   $55.32   $55.30   $55.30  
  Purchase #7 $74.75   7.754%   $80.5461   $80.55   $80.55   $80.50  
  7 purchase totals = $853.96       $901.1610   $901.16   $901.15   $901.10