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 $46.47   6.740%   $49.6021   $49.60   $49.60   $49.60  
  Purchase #2 $201.72   8.346%   $218.5556   $218.56   $218.55   $218.60  
  Purchase #3 $59.27   13.614%   $67.339   $67.34   $67.35   $67.30  
  Purchase #4 $69.79   11.699%   $77.9547   $77.95   $77.95   $78.00  
  Purchase #5 $13.96   3.380%   $14.4318   $14.43   $14.45   $14.40  
  Purchase #6 $152.44   9.202%   $166.4675   $166.47   $166.45   $166.50  
  Purchase #7 $184.41   10.530%   $203.8284   $203.83   $203.85   $203.80  
  7 purchase totals = $728.06       $798.1791   $798.18   $798.20   $798.20