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 $219.51   12.544%   $247.0453   $247.05   $247.05   $247.00  
  Purchase #2 $76.74   4.503%   $80.1956   $80.20   $80.20   $80.20  
  Purchase #3 $171.68   11.478%   $191.3854   $191.39   $191.40   $191.40  
  Purchase #4 $86.65   3.285%   $89.4965   $89.50   $89.50   $89.50  
  Purchase #5 $200.76   8.399%   $217.6218   $217.62   $217.60   $217.60  
  Purchase #6 $187.89   12.839%   $212.0132   $212.01   $212.00   $212.00  
  Purchase #7 $61.90   11.453%   $68.9894   $68.99   $69.00   $69.00  
  7 purchase totals = $1,005.13       $1,106.7472   $1,106.76   $1,106.75   $1,106.70