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 $61.61   12.707%   $69.4388   $69.44   $69.45   $69.40  
  Purchase #2 $232.42   7.343%   $249.4866   $249.49   $249.50   $249.50  
  Purchase #3 $126.28   12.720%   $142.3428   $142.34   $142.35   $142.30  
  Purchase #4 $77.49   9.644%   $84.9631   $84.96   $84.95   $85.00  
  Purchase #5 $174.96   8.322%   $189.5202   $189.52   $189.50   $189.50  
  Purchase #6 $225.75   4.718%   $236.4009   $236.40   $236.40   $236.40  
  Purchase #7 $82.72   13.124%   $93.5762   $93.58   $93.60   $93.60  
  7 purchase totals = $981.23       $1,065.7286   $1,065.73   $1,065.75   $1,065.70