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 $84.97   13.838%   $96.7281   $96.73   $96.75   $96.70  
  Purchase #2 $189.72   11.277%   $211.1147   $211.11   $211.10   $211.10  
  Purchase #3 $50.63   10.110%   $55.7487   $55.75   $55.75   $55.70  
  Purchase #4 $187.77   7.782%   $202.3823   $202.38   $202.40   $202.40  
  Purchase #5 $53.54   4.780%   $56.0992   $56.10   $56.10   $56.10  
  Purchase #6 $38.96   13.321%   $44.1499   $44.15   $44.15   $44.10  
  Purchase #7 $240.82   10.291%   $265.6028   $265.60   $265.60   $265.60  
  7 purchase totals = $846.41       $931.8257   $931.82   $931.85   $931.70