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 $38.94   13.216%   $44.0863   $44.09   $44.10   $44.10  
  Purchase #2 $168.93   6.509%   $179.9257   $179.93   $179.95   $179.90  
  Purchase #3 $84.27   5.581%   $88.9731   $88.97   $88.95   $89.00  
  Purchase #4 $245.58   10.152%   $270.5113   $270.51   $270.50   $270.50  
  Purchase #5 $172.44   5.362%   $181.6862   $181.69   $181.70   $181.70  
  Purchase #6 $46.91   8.676%   $50.9799   $50.98   $51.00   $51.00  
  Purchase #7 $210.58   9.595%   $230.7852   $230.79   $230.80   $230.80  
  7 purchase totals = $967.65       $1,046.9477   $1,046.96   $1,047.00   $1,047.00