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 $215.80   8.496%   $234.1344   $234.13   $234.15   $234.10  
  Purchase #2 $223.58   6.734%   $238.6359   $238.64   $238.65   $238.60  
  Purchase #3 $180.35   8.697%   $196.035   $196.04   $196.05   $196.00  
  Purchase #4 $22.33   6.359%   $23.75   $23.75   $23.75   $23.80  
  Purchase #5 $16.60   11.439%   $18.4989   $18.50   $18.50   $18.50  
  Purchase #6 $129.90   13.406%   $147.3144   $147.31   $147.30   $147.30  
  Purchase #7 $149.69   13.271%   $169.5554   $169.56   $169.55   $169.60  
  7 purchase totals = $938.25       $1,027.9240   $1,027.93   $1,027.95   $1,027.90