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 $140.94   9.709%   $154.6239   $154.62   $154.60   $154.60  
  Purchase #2 $160.51   8.132%   $173.5627   $173.56   $173.55   $173.60  
  Purchase #3 $74.60   3.244%   $77.02   $77.02   $77.00   $77.00  
  Purchase #4 $242.29   8.317%   $262.4413   $262.44   $262.45   $262.40  
  Purchase #5 $24.65   6.621%   $26.2821   $26.28   $26.30   $26.30  
  Purchase #6 $58.69   4.539%   $61.3539   $61.35   $61.35   $61.40  
  Purchase #7 $85.95   5.428%   $90.6154   $90.62   $90.60   $90.60  
  7 purchase totals = $787.63       $845.8993   $845.89   $845.85   $845.90