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 $191.62   7.146%   $205.3132   $205.31   $205.30   $205.30  
  Purchase #2 $208.70   4.415%   $217.9141   $217.91   $217.90   $217.90  
  Purchase #3 $110.71   7.228%   $118.7121   $118.71   $118.70   $118.70  
  Purchase #4 $122.66   6.855%   $131.0683   $131.07   $131.05   $131.10  
  Purchase #5 $75.61   13.112%   $85.524   $85.52   $85.50   $85.50  
  Purchase #6 $32.52   4.405%   $33.9525   $33.95   $33.95   $34.00  
  Purchase #7 $218.25   7.542%   $234.7104   $234.71   $234.70   $234.70  
  7 purchase totals = $960.07       $1,027.1946   $1,027.18   $1,027.10   $1,027.20