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 $244.88   6.503%   $260.8045   $260.80   $260.80   $260.80  
  Purchase #2 $103.68   8.650%   $112.6483   $112.65   $112.65   $112.60  
  Purchase #3 $148.34   12.635%   $167.0828   $167.08   $167.10   $167.10  
  Purchase #4 $49.67   10.508%   $54.8893   $54.89   $54.90   $54.90  
  Purchase #5 $60.58   8.868%   $65.9522   $65.95   $65.95   $66.00  
  Purchase #6 $180.64   10.320%   $199.282   $199.28   $199.30   $199.30  
  Purchase #7 $152.55   10.136%   $168.0125   $168.01   $168.00   $168.00  
  7 purchase totals = $940.34       $1,028.6716   $1,028.66   $1,028.70   $1,028.70