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 $94.51   5.571%   $99.7752   $99.78   $99.80   $99.80  
  Purchase #2 $167.58   5.493%   $176.7852   $176.79   $176.80   $176.80  
  Purchase #3 $228.88   12.295%   $257.0208   $257.02   $257.00   $257.00  
  Purchase #4 $250.91   11.839%   $280.6152   $280.62   $280.60   $280.60  
  Purchase #5 $209.30   13.871%   $238.332   $238.33   $238.35   $238.30  
  Purchase #6 $180.79   9.182%   $197.3901   $197.39   $197.40   $197.40  
  Purchase #7 $69.31   5.865%   $73.375   $73.38   $73.40   $73.40  
  7 purchase totals = $1,201.28       $1,323.2935   $1,323.31   $1,323.35   $1,323.30