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 $231.67   13.336%   $262.5655   $262.57   $262.55   $262.60  
  Purchase #2 $59.27   12.745%   $66.824   $66.82   $66.80   $66.80  
  Purchase #3 $69.56   8.695%   $75.6082   $75.61   $75.60   $75.60  
  Purchase #4 $168.60   6.734%   $179.9535   $179.95   $179.95   $180.00  
  Purchase #5 $178.90   12.174%   $200.6793   $200.68   $200.70   $200.70  
  Purchase #6 $144.80   10.773%   $160.3993   $160.40   $160.40   $160.40  
  Purchase #7 $130.54   6.325%   $138.7967   $138.80   $138.80   $138.80  
  7 purchase totals = $983.34       $1,084.8265   $1,084.83   $1,084.80   $1,084.90