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 $89.95   6.278%   $95.5971   $95.60   $95.60   $95.60  
  Purchase #2 $62.57   7.636%   $67.3478   $67.35   $67.35   $67.30  
  Purchase #3 $216.46   11.678%   $241.7382   $241.74   $241.75   $241.70  
  Purchase #4 $208.43   11.283%   $231.9472   $231.95   $231.95   $231.90  
  Purchase #5 $63.31   9.142%   $69.0978   $69.10   $69.10   $69.10  
  Purchase #6 $8.42   13.600%   $9.5651   $9.57   $9.55   $9.60  
  Purchase #7 $23.46   12.830%   $26.4699   $26.47   $26.45   $26.50  
  7 purchase totals = $672.60       $741.7631   $741.78   $741.75   $741.70