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 $157.39   6.144%   $167.06   $167.06   $167.05   $167.10  
  Purchase #2 $68.93   4.686%   $72.1601   $72.16   $72.15   $72.20  
  Purchase #3 $234.70   12.209%   $263.3545   $263.35   $263.35   $263.40  
  Purchase #4 $186.80   8.123%   $201.9738   $201.97   $201.95   $202.00  
  Purchase #5 $28.35   13.799%   $32.262   $32.26   $32.25   $32.30  
  Purchase #6 $207.33   3.457%   $214.4974   $214.50   $214.50   $214.50  
  Purchase #7 $192.52   10.277%   $212.3053   $212.31   $212.30   $212.30  
  7 purchase totals = $1,076.02       $1,163.6131   $1,163.61   $1,163.55   $1,163.80