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 $165.44   12.872%   $186.7354   $186.74   $186.75   $186.70  
  Purchase #2 $48.38   8.163%   $52.3293   $52.33   $52.35   $52.30  
  Purchase #3 $245.71   8.672%   $267.018   $267.02   $267.00   $267.00  
  Purchase #4 $77.33   9.551%   $84.7158   $84.72   $84.70   $84.70  
  Purchase #5 $220.80   6.726%   $235.651   $235.65   $235.65   $235.70  
  Purchase #6 $84.92   13.314%   $96.2262   $96.23   $96.25   $96.20  
  Purchase #7 $228.74   5.240%   $240.726   $240.73   $240.75   $240.70  
  7 purchase totals = $1,071.32       $1,163.4017   $1,163.42   $1,163.45   $1,163.30