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 $235.46   4.395%   $245.8085   $245.81   $245.80   $245.80  
  Purchase #2 $211.44   6.651%   $225.5029   $225.50   $225.50   $225.50  
  Purchase #3 $75.99   5.181%   $79.927   $79.93   $79.95   $79.90  
  Purchase #4 $62.87   8.136%   $67.9851   $67.99   $68.00   $68.00  
  Purchase #5 $54.54   9.420%   $59.6777   $59.68   $59.70   $59.70  
  Purchase #6 $238.33   11.769%   $266.3791   $266.38   $266.40   $266.40  
  Purchase #7 $47.55   9.398%   $52.0187   $52.02   $52.00   $52.00  
  7 purchase totals = $926.18       $997.2990   $997.31   $997.35   $997.30