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 $191.78   6.177%   $203.6263   $203.63   $203.65   $203.60  
  Purchase #2 $69.38   6.653%   $73.9959   $74.00   $74.00   $74.00  
  Purchase #3 $50.28   5.211%   $52.9001   $52.90   $52.90   $52.90  
  Purchase #4 $177.30   8.534%   $192.4308   $192.43   $192.45   $192.40  
  Purchase #5 $176.37   8.280%   $190.9734   $190.97   $190.95   $191.00  
  Purchase #6 $95.99   12.317%   $107.8131   $107.81   $107.80   $107.80  
  Purchase #7 $221.91   7.449%   $238.4401   $238.44   $238.45   $238.40  
  7 purchase totals = $983.01       $1,060.1797   $1,060.18   $1,060.20   $1,060.10