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 $61.51   12.409%   $69.1428   $69.14   $69.15   $69.10  
  Purchase #2 $243.97   10.749%   $270.1943   $270.19   $270.20   $270.20  
  Purchase #3 $242.80   4.842%   $254.5564   $254.56   $254.55   $254.60  
  Purchase #4 $182.35   11.590%   $203.4844   $203.48   $203.50   $203.50  
  Purchase #5 $83.28   3.170%   $85.92   $85.92   $85.90   $85.90  
  Purchase #6 $234.98   4.189%   $244.8233   $244.82   $244.80   $244.80  
  Purchase #7 $226.26   7.786%   $243.8766   $243.88   $243.90   $243.90  
  7 purchase totals = $1,275.15       $1,371.9978   $1,371.99   $1,372.00   $1,372.00