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 $63.67   8.861%   $69.3118   $69.31   $69.30   $69.30  
  Purchase #2 $10.40   5.742%   $10.9972   $11.00   $11.00   $11.00  
  Purchase #3 $237.94   8.236%   $257.5367   $257.54   $257.55   $257.50  
  Purchase #4 $179.49   11.868%   $200.7919   $200.79   $200.80   $200.80  
  Purchase #5 $74.67   12.579%   $84.0627   $84.06   $84.05   $84.10  
  Purchase #6 $50.31   7.413%   $54.0395   $54.04   $54.05   $54.00  
  Purchase #7 $61.25   5.689%   $64.7345   $64.73   $64.75   $64.70  
  7 purchase totals = $677.73       $741.4743   $741.47   $741.50   $741.40