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 $5.60   4.436%   $5.8484   $5.85   $5.85   $5.80  
  Purchase #2 $200.70   5.630%   $211.9994   $212.00   $212.00   $212.00  
  Purchase #3 $39.58   13.400%   $44.8837   $44.88   $44.90   $44.90  
  Purchase #4 $47.71   11.287%   $53.095   $53.10   $53.10   $53.10  
  Purchase #5 $128.72   10.141%   $141.7735   $141.77   $141.75   $141.80  
  Purchase #6 $35.99   10.400%   $39.733   $39.73   $39.75   $39.70  
  Purchase #7 $181.84   11.520%   $202.788   $202.79   $202.80   $202.80  
  7 purchase totals = $640.14       $700.1210   $700.12   $700.15   $700.10