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 $153.71   6.504%   $163.7073   $163.71   $163.70   $163.70  
  Purchase #2 $24.27   5.104%   $25.5087   $25.51   $25.50   $25.50  
  Purchase #3 $245.34   7.229%   $263.0756   $263.08   $263.10   $263.10  
  Purchase #4 $229.34   10.212%   $252.7602   $252.76   $252.75   $252.80  
  Purchase #5 $194.88   4.244%   $203.1507   $203.15   $203.15   $203.20  
  Purchase #6 $35.61   7.805%   $38.3894   $38.39   $38.40   $38.40  
  Purchase #7 $71.50   5.545%   $75.4647   $75.46   $75.45   $75.50  
  7 purchase totals = $954.65       $1,022.0566   $1,022.06   $1,022.05   $1,022.20