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 $204.78   13.650%   $232.7325   $232.73   $232.75   $232.70  
  Purchase #2 $228.81   3.546%   $236.9236   $236.92   $236.90   $236.90  
  Purchase #3 $68.53   10.461%   $75.6989   $75.70   $75.70   $75.70  
  Purchase #4 $49.59   5.754%   $52.4434   $52.44   $52.45   $52.40  
  Purchase #5 $248.78   4.783%   $260.6791   $260.68   $260.70   $260.70  
  Purchase #6 $96.88   6.640%   $103.3128   $103.31   $103.30   $103.30  
  Purchase #7 $126.88   7.863%   $136.8566   $136.86   $136.85   $136.90  
  7 purchase totals = $1,024.25       $1,098.6469   $1,098.64   $1,098.65   $1,098.60