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 $245.99   9.362%   $269.0196   $269.02   $269.00   $269.00  
  Purchase #2 $23.94   3.668%   $24.8181   $24.82   $24.80   $24.80  
  Purchase #3 $225.32   3.206%   $232.5438   $232.54   $232.55   $232.50  
  Purchase #4 $41.50   7.174%   $44.4772   $44.48   $44.50   $44.50  
  Purchase #5 $83.47   8.545%   $90.6025   $90.60   $90.60   $90.60  
  Purchase #6 $176.84   12.350%   $198.6797   $198.68   $198.70   $198.70  
  Purchase #7 $132.93   13.178%   $150.4475   $150.45   $150.45   $150.40  
  7 purchase totals = $929.99       $1,010.5884   $1,010.59   $1,010.60   $1,010.50