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 $68.58   12.704%   $77.2924   $77.29   $77.30   $77.30  
  Purchase #2 $194.65   6.192%   $206.7027   $206.70   $206.70   $206.70  
  Purchase #3 $211.31   4.614%   $221.0598   $221.06   $221.05   $221.10  
  Purchase #4 $244.67   9.559%   $268.058   $268.06   $268.05   $268.10  
  Purchase #5 $214.62   5.357%   $226.1172   $226.12   $226.10   $226.10  
  Purchase #6 $124.81   4.650%   $130.6137   $130.61   $130.60   $130.60  
  Purchase #7 $197.85   13.751%   $225.0564   $225.06   $225.05   $225.10  
  7 purchase totals = $1,256.49       $1,354.9002   $1,354.90   $1,354.85   $1,355.00