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 $179.46   13.403%   $203.513   $203.51   $203.50   $203.50  
  Purchase #2 $218.58   9.349%   $239.015   $239.02   $239.00   $239.00  
  Purchase #3 $134.75   8.178%   $145.7699   $145.77   $145.75   $145.80  
  Purchase #4 $17.68   5.143%   $18.5893   $18.59   $18.60   $18.60  
  Purchase #5 $181.55   11.780%   $202.9366   $202.94   $202.95   $202.90  
  Purchase #6 $169.26   7.781%   $182.4301   $182.43   $182.45   $182.40  
  Purchase #7 $46.55   9.614%   $51.0253   $51.03   $51.05   $51.00  
  7 purchase totals = $947.83       $1,043.2792   $1,043.29   $1,043.30   $1,043.20