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 $67.54   3.544%   $69.9336   $69.93   $69.95   $69.90  
  Purchase #2 $201.75   9.515%   $220.9465   $220.95   $220.95   $220.90  
  Purchase #3 $126.44   6.146%   $134.211   $134.21   $134.20   $134.20  
  Purchase #4 $222.92   12.805%   $251.4649   $251.46   $251.45   $251.50  
  Purchase #5 $20.47   5.586%   $21.6135   $21.61   $21.60   $21.60  
  Purchase #6 $43.33   5.387%   $45.6642   $45.66   $45.65   $45.70  
  Purchase #7 $196.62   7.377%   $211.1247   $211.12   $211.10   $211.10  
  7 purchase totals = $879.07       $954.9584   $954.94   $954.90   $954.90