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 $30.89   9.647%   $33.87   $33.87   $33.85   $33.90  
  Purchase #2 $210.64   4.271%   $219.6364   $219.64   $219.65   $219.60  
  Purchase #3 $148.43   8.187%   $160.582   $160.58   $160.60   $160.60  
  Purchase #4 $61.43   6.368%   $65.3419   $65.34   $65.35   $65.30  
  Purchase #5 $71.65   11.260%   $79.7178   $79.72   $79.70   $79.70  
  Purchase #6 $239.59   11.251%   $266.5463   $266.55   $266.55   $266.50  
  Purchase #7 $57.41   9.803%   $63.0379   $63.04   $63.05   $63.00  
  7 purchase totals = $820.04       $888.7323   $888.74   $888.75   $888.60