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 $250.40   10.534%   $276.7771   $276.78   $276.80   $276.80  
  Purchase #2 $62.75   3.591%   $65.0034   $65.00   $65.00   $65.00  
  Purchase #3 $239.74   13.759%   $272.7258   $272.73   $272.75   $272.70  
  Purchase #4 $118.70   7.662%   $127.7948   $127.79   $127.80   $127.80  
  Purchase #5 $175.75   13.200%   $198.949   $198.95   $198.95   $198.90  
  Purchase #6 $37.39   5.523%   $39.455   $39.46   $39.45   $39.50  
  Purchase #7 $91.64   11.627%   $102.295   $102.30   $102.30   $102.30  
  7 purchase totals = $976.37       $1,083.0001   $1,083.01   $1,083.05   $1,083.00