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 $60.61   8.461%   $65.7382   $65.74   $65.75   $65.70  
  Purchase #2 $141.46   10.803%   $156.7419   $156.74   $156.75   $156.70  
  Purchase #3 $226.58   8.779%   $246.4715   $246.47   $246.45   $246.50  
  Purchase #4 $165.86   6.459%   $176.5729   $176.57   $176.55   $176.60  
  Purchase #5 $246.78   12.196%   $276.8773   $276.88   $276.90   $276.90  
  Purchase #6 $84.39   4.110%   $87.8584   $87.86   $87.85   $87.90  
  Purchase #7 $33.25   13.280%   $37.6656   $37.67   $37.65   $37.70  
  7 purchase totals = $958.93       $1,047.9258   $1,047.93   $1,047.90   $1,048.00