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 $78.74   8.834%   $85.6959   $85.70   $85.70   $85.70  
  Purchase #2 $246.57   9.248%   $269.3728   $269.37   $269.35   $269.40  
  Purchase #3 $35.59   4.872%   $37.3239   $37.32   $37.30   $37.30  
  Purchase #4 $84.29   11.434%   $93.9277   $93.93   $93.95   $93.90  
  Purchase #5 $174.57   13.456%   $198.0601   $198.06   $198.05   $198.10  
  Purchase #6 $6.69   7.725%   $7.2068   $7.21   $7.20   $7.20  
  Purchase #7 $148.74   4.503%   $155.4378   $155.44   $155.45   $155.40  
  7 purchase totals = $775.19       $847.0250   $847.03   $847.00   $847.00