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 $118.28   5.332%   $124.5867   $124.59   $124.60   $124.60  
  Purchase #2 $23.25   8.283%   $25.1758   $25.18   $25.20   $25.20  
  Purchase #3 $10.38   4.761%   $10.8742   $10.87   $10.85   $10.90  
  Purchase #4 $124.55   4.825%   $130.5595   $130.56   $130.55   $130.60  
  Purchase #5 $32.32   9.714%   $35.4596   $35.46   $35.45   $35.50  
  Purchase #6 $147.53   12.816%   $166.4374   $166.44   $166.45   $166.40  
  Purchase #7 $65.64   3.746%   $68.0989   $68.10   $68.10   $68.10  
  7 purchase totals = $521.95       $561.1921   $561.20   $561.20   $561.30