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 $84.57   13.758%   $96.2051   $96.21   $96.20   $96.20  
  Purchase #2 $79.52   8.371%   $86.1766   $86.18   $86.20   $86.20  
  Purchase #3 $185.84   11.784%   $207.7394   $207.74   $207.75   $207.70  
  Purchase #4 $41.86   12.560%   $47.1176   $47.12   $47.10   $47.10  
  Purchase #5 $83.43   6.865%   $89.1575   $89.16   $89.15   $89.20  
  Purchase #6 $96.84   10.722%   $107.2232   $107.22   $107.20   $107.20  
  Purchase #7 $212.65   10.711%   $235.4269   $235.43   $235.45   $235.40  
  7 purchase totals = $784.71       $869.0463   $869.06   $869.05   $869.00