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 $68.30   12.576%   $76.8894   $76.89   $76.90   $76.90  
  Purchase #2 $178.80   8.320%   $193.6762   $193.68   $193.70   $193.70  
  Purchase #3 $95.96   11.329%   $106.8313   $106.83   $106.85   $106.80  
  Purchase #4 $25.74   6.211%   $27.3387   $27.34   $27.35   $27.30  
  Purchase #5 $175.26   12.401%   $196.994   $196.99   $197.00   $197.00  
  Purchase #6 $189.31   3.566%   $196.0608   $196.06   $196.05   $196.10  
  Purchase #7 $165.45   4.251%   $172.4833   $172.48   $172.50   $172.50  
  7 purchase totals = $898.82       $970.2737   $970.27   $970.35   $970.30