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 $24.61   7.785%   $26.5259   $26.53   $26.55   $26.50  
  Purchase #2 $194.69   3.257%   $201.0311   $201.03   $201.05   $201.00  
  Purchase #3 $147.47   5.487%   $155.5617   $155.56   $155.55   $155.60  
  Purchase #4 $205.47   10.278%   $226.5882   $226.59   $226.60   $226.60  
  Purchase #5 $246.46   3.578%   $255.2783   $255.28   $255.30   $255.30  
  Purchase #6 $117.67   5.387%   $124.0089   $124.01   $124.00   $124.00  
  Purchase #7 $75.88   12.326%   $85.233   $85.23   $85.25   $85.20  
  7 purchase totals = $1,012.25       $1,074.2271   $1,074.23   $1,074.30   $1,074.20