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 $61.71   7.675%   $66.4462   $66.45   $66.45   $66.40  
  Purchase #2 $222.94   6.405%   $237.2193   $237.22   $237.20   $237.20  
  Purchase #3 $211.43   8.299%   $228.9766   $228.98   $229.00   $229.00  
  Purchase #4 $43.88   6.765%   $46.8485   $46.85   $46.85   $46.80  
  Purchase #5 $105.49   13.288%   $119.5075   $119.51   $119.50   $119.50  
  Purchase #6 $52.28   8.386%   $56.6642   $56.66   $56.65   $56.70  
  Purchase #7 $144.88   4.211%   $150.9809   $150.98   $151.00   $151.00  
  7 purchase totals = $842.61       $906.6432   $906.65   $906.65   $906.60