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 $241.49   11.571%   $269.4328   $269.43   $269.45   $269.40  
  Purchase #2 $23.78   12.136%   $26.6659   $26.67   $26.65   $26.70  
  Purchase #3 $28.26   4.393%   $29.5015   $29.50   $29.50   $29.50  
  Purchase #4 $121.64   10.291%   $134.158   $134.16   $134.15   $134.20  
  Purchase #5 $148.64   12.398%   $167.0684   $167.07   $167.05   $167.10  
  Purchase #6 $235.68   7.764%   $253.9782   $253.98   $254.00   $254.00  
  Purchase #7 $59.25   10.152%   $65.2651   $65.27   $65.25   $65.30  
  7 purchase totals = $858.74       $946.0699   $946.08   $946.05   $946.20