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 $62.92   6.724%   $67.1507   $67.15   $67.15   $67.20  
  Purchase #2 $218.70   10.173%   $240.9484   $240.95   $240.95   $240.90  
  Purchase #3 $54.33   13.528%   $61.6798   $61.68   $61.70   $61.70  
  Purchase #4 $238.35   6.278%   $253.3136   $253.31   $253.30   $253.30  
  Purchase #5 $65.97   6.559%   $70.297   $70.30   $70.30   $70.30  
  Purchase #6 $24.95   3.356%   $25.7873   $25.79   $25.80   $25.80  
  Purchase #7 $147.38   11.818%   $164.7974   $164.80   $164.80   $164.80  
  7 purchase totals = $812.60       $883.9742   $883.98   $884.00   $884.00