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 $89.72   6.263%   $95.3392   $95.34   $95.35   $95.30  
  Purchase #2 $57.67   13.592%   $65.5085   $65.51   $65.50   $65.50  
  Purchase #3 $201.25   6.563%   $214.458   $214.46   $214.45   $214.50  
  Purchase #4 $247.92   6.692%   $264.5108   $264.51   $264.50   $264.50  
  Purchase #5 $149.98   10.316%   $165.4519   $165.45   $165.45   $165.50  
  Purchase #6 $152.99   11.527%   $170.6252   $170.63   $170.65   $170.60  
  Purchase #7 $236.60   6.803%   $252.6959   $252.70   $252.70   $252.70  
  7 purchase totals = $1,136.13       $1,228.5895   $1,228.60   $1,228.60   $1,228.60