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 $136.64   12.400%   $153.5834   $153.58   $153.60   $153.60  
  Purchase #2 $61.67   11.438%   $68.7238   $68.72   $68.70   $68.70  
  Purchase #3 $234.33   9.309%   $256.1438   $256.14   $256.15   $256.10  
  Purchase #4 $203.69   3.822%   $211.475   $211.48   $211.50   $211.50  
  Purchase #5 $124.97   8.817%   $135.9886   $135.99   $136.00   $136.00  
  Purchase #6 $62.99   4.609%   $65.8932   $65.89   $65.90   $65.90  
  Purchase #7 $109.76   10.668%   $121.4692   $121.47   $121.45   $121.50  
  7 purchase totals = $934.05       $1,013.2770   $1,013.27   $1,013.30   $1,013.30