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 $205.30   11.338%   $228.5769   $228.58   $228.60   $228.60  
  Purchase #2 $73.85   3.457%   $76.403   $76.40   $76.40   $76.40  
  Purchase #3 $38.62   10.655%   $42.735   $42.74   $42.75   $42.70  
  Purchase #4 $211.45   12.175%   $237.194   $237.19   $237.20   $237.20  
  Purchase #5 $195.32   8.173%   $211.2835   $211.28   $211.30   $211.30  
  Purchase #6 $237.92   12.437%   $267.5101   $267.51   $267.50   $267.50  
  Purchase #7 $28.89   10.128%   $31.816   $31.82   $31.80   $31.80  
  7 purchase totals = $991.35       $1,095.5185   $1,095.52   $1,095.55   $1,095.50