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 $247.80   4.816%   $259.734   $259.73   $259.75   $259.70  
  Purchase #2 $63.49   4.775%   $66.5216   $66.52   $66.50   $66.50  
  Purchase #3 $171.36   3.569%   $177.4758   $177.48   $177.50   $177.50  
  Purchase #4 $185.83   12.448%   $208.9621   $208.96   $208.95   $209.00  
  Purchase #5 $41.74   10.570%   $46.1519   $46.15   $46.15   $46.20  
  Purchase #6 $91.60   13.869%   $104.304   $104.30   $104.30   $104.30  
  Purchase #7 $174.75   9.568%   $191.4701   $191.47   $191.45   $191.50  
  7 purchase totals = $976.57       $1,054.6195   $1,054.61   $1,054.60   $1,054.70