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 $186.36   10.351%   $205.6501   $205.65   $205.65   $205.70  
  Purchase #2 $213.49   10.545%   $236.0025   $236.00   $236.00   $236.00  
  Purchase #3 $196.72   6.550%   $209.6052   $209.61   $209.60   $209.60  
  Purchase #4 $41.62   13.663%   $47.3065   $47.31   $47.30   $47.30  
  Purchase #5 $149.45   3.711%   $154.9961   $155.00   $155.00   $155.00  
  Purchase #6 $83.85   11.473%   $93.4701   $93.47   $93.45   $93.50  
  Purchase #7 $81.96   7.251%   $87.9029   $87.90   $87.90   $87.90  
  7 purchase totals = $953.45       $1,034.9334   $1,034.94   $1,034.90   $1,035.00