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 $229.58   10.278%   $253.1762   $253.18   $253.20   $253.20  
  Purchase #2 $138.55   13.296%   $156.9716   $156.97   $156.95   $157.00  
  Purchase #3 $97.82   4.856%   $102.5701   $102.57   $102.55   $102.60  
  Purchase #4 $135.46   10.310%   $149.4259   $149.43   $149.45   $149.40  
  Purchase #5 $55.86   8.584%   $60.655   $60.66   $60.65   $60.70  
  Purchase #6 $36.57   7.695%   $39.3841   $39.38   $39.40   $39.40  
  Purchase #7 $244.71   7.831%   $263.8732   $263.87   $263.85   $263.90  
  7 purchase totals = $938.55       $1,026.0561   $1,026.06   $1,026.05   $1,026.20