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 $194.88   8.788%   $212.0061   $212.01   $212.00   $212.00  
  Purchase #2 $127.53   13.459%   $144.6943   $144.69   $144.70   $144.70  
  Purchase #3 $25.35   3.518%   $26.2418   $26.24   $26.25   $26.20  
  Purchase #4 $86.42   5.809%   $91.4401   $91.44   $91.45   $91.40  
  Purchase #5 $202.87   7.579%   $218.2455   $218.25   $218.25   $218.20  
  Purchase #6 $127.72   8.578%   $138.6758   $138.68   $138.70   $138.70  
  Purchase #7 $19.58   9.778%   $21.4945   $21.49   $21.50   $21.50  
  7 purchase totals = $784.35       $852.7981   $852.80   $852.85   $852.70