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 $64.27   8.207%   $69.5446   $69.54   $69.55   $69.50  
  Purchase #2 $109.58   13.478%   $124.3492   $124.35   $124.35   $124.30  
  Purchase #3 $196.50   12.845%   $221.7404   $221.74   $221.75   $221.70  
  Purchase #4 $225.95   8.591%   $245.3614   $245.36   $245.35   $245.40  
  Purchase #5 $209.37   9.362%   $228.9712   $228.97   $228.95   $229.00  
  Purchase #6 $106.43   4.805%   $111.544   $111.54   $111.55   $111.50  
  Purchase #7 $14.38   10.653%   $15.9119   $15.91   $15.90   $15.90  
  7 purchase totals = $926.48       $1,017.4227   $1,017.41   $1,017.40   $1,017.30