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 $126.38   12.360%   $142.0006   $142.00   $142.00   $142.00  
  Purchase #2 $71.54   13.861%   $81.4562   $81.46   $81.45   $81.50  
  Purchase #3 $224.96   8.133%   $243.256   $243.26   $243.25   $243.30  
  Purchase #4 $186.95   6.751%   $199.571   $199.57   $199.55   $199.60  
  Purchase #5 $183.78   4.733%   $192.4783   $192.48   $192.50   $192.50  
  Purchase #6 $58.66   13.660%   $66.673   $66.67   $66.65   $66.70  
  Purchase #7 $172.42   9.811%   $189.3361   $189.34   $189.35   $189.30  
  7 purchase totals = $1,024.69       $1,114.7712   $1,114.78   $1,114.75   $1,114.90