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 $203.65   13.864%   $231.884   $231.88   $231.90   $231.90  
  Purchase #2 $76.85   13.561%   $87.2716   $87.27   $87.25   $87.30  
  Purchase #3 $109.97   6.730%   $117.371   $117.37   $117.35   $117.40  
  Purchase #4 $55.79   13.279%   $63.1984   $63.20   $63.20   $63.20  
  Purchase #5 $162.52   7.216%   $174.2474   $174.25   $174.25   $174.20  
  Purchase #6 $180.51   13.870%   $205.5467   $205.55   $205.55   $205.50  
  Purchase #7 $152.85   7.275%   $163.9698   $163.97   $163.95   $164.00  
  7 purchase totals = $942.14       $1,043.4889   $1,043.49   $1,043.45   $1,043.50