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 $160.49   4.176%   $167.1921   $167.19   $167.20   $167.20  
  Purchase #2 $118.86   9.293%   $129.9057   $129.91   $129.90   $129.90  
  Purchase #3 $49.92   12.155%   $55.9878   $55.99   $56.00   $56.00  
  Purchase #4 $201.36   8.605%   $218.687   $218.69   $218.70   $218.70  
  Purchase #5 $243.71   12.399%   $273.9276   $273.93   $273.95   $273.90  
  Purchase #6 $93.91   13.237%   $106.3409   $106.34   $106.35   $106.30  
  Purchase #7 $128.79   11.667%   $143.8159   $143.82   $143.80   $143.80  
  7 purchase totals = $997.04       $1,095.8570   $1,095.87   $1,095.90   $1,095.80