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 $95.95   12.596%   $108.0359   $108.04   $108.05   $108.00  
  Purchase #2 $219.98   5.793%   $232.7234   $232.72   $232.70   $232.70  
  Purchase #3 $61.46   3.808%   $63.8004   $63.80   $63.80   $63.80  
  Purchase #4 $221.56   13.245%   $250.9056   $250.91   $250.90   $250.90  
  Purchase #5 $137.54   5.315%   $144.8503   $144.85   $144.85   $144.90  
  Purchase #6 $169.70   10.308%   $187.1927   $187.19   $187.20   $187.20  
  Purchase #7 $11.42   10.436%   $12.6118   $12.61   $12.60   $12.60  
  7 purchase totals = $917.61       $1,000.1201   $1,000.12   $1,000.10   $1,000.10