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 $234.99   13.657%   $267.0826   $267.08   $267.10   $267.10  
  Purchase #2 $186.52   4.464%   $194.8463   $194.85   $194.85   $194.80  
  Purchase #3 $44.37   9.491%   $48.5812   $48.58   $48.60   $48.60  
  Purchase #4 $69.79   12.157%   $78.2744   $78.27   $78.25   $78.30  
  Purchase #5 $196.47   3.138%   $202.6352   $202.64   $202.65   $202.60  
  Purchase #6 $90.79   5.806%   $96.0613   $96.06   $96.05   $96.10  
  Purchase #7 $157.67   13.181%   $178.4525   $178.45   $178.45   $178.50  
  7 purchase totals = $980.60       $1,065.9335   $1,065.93   $1,065.95   $1,066.00