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 $58.41   12.431%   $65.6709   $65.67   $65.65   $65.70  
  Purchase #2 $192.28   10.289%   $212.0637   $212.06   $212.05   $212.10  
  Purchase #3 $180.36   8.593%   $195.8583   $195.86   $195.85   $195.90  
  Purchase #4 $21.93   13.383%   $24.8649   $24.86   $24.85   $24.90  
  Purchase #5 $189.55   6.521%   $201.9106   $201.91   $201.90   $201.90  
  Purchase #6 $245.63   8.434%   $266.3464   $266.35   $266.35   $266.30  
  Purchase #7 $163.80   12.716%   $184.6288   $184.63   $184.65   $184.60  
  7 purchase totals = $1,051.96       $1,151.3436   $1,151.34   $1,151.30   $1,151.40