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 $227.51   13.464%   $258.1419   $258.14   $258.15   $258.10  
  Purchase #2 $211.55   9.335%   $231.2982   $231.30   $231.30   $231.30  
  Purchase #3 $49.66   11.291%   $55.2671   $55.27   $55.25   $55.30  
  Purchase #4 $162.36   4.144%   $169.0882   $169.09   $169.10   $169.10  
  Purchase #5 $92.59   12.372%   $104.0452   $104.05   $104.05   $104.00  
  Purchase #6 $232.54   8.524%   $252.3617   $252.36   $252.35   $252.40  
  Purchase #7 $57.88   7.255%   $62.0792   $62.08   $62.10   $62.10  
  7 purchase totals = $1,034.09       $1,132.2815   $1,132.29   $1,132.30   $1,132.30