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 $157.81   13.793%   $179.5767   $179.58   $179.60   $179.60  
  Purchase #2 $59.60   6.149%   $63.2648   $63.26   $63.25   $63.30  
  Purchase #3 $134.26   13.448%   $152.3153   $152.32   $152.30   $152.30  
  Purchase #4 $64.80   3.530%   $67.0874   $67.09   $67.10   $67.10  
  Purchase #5 $25.55   12.613%   $28.7726   $28.77   $28.75   $28.80  
  Purchase #6 $99.87   8.850%   $108.7085   $108.71   $108.70   $108.70  
  Purchase #7 $156.68   3.793%   $162.6229   $162.62   $162.60   $162.60  
  7 purchase totals = $698.57       $762.3482   $762.35   $762.30   $762.40