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 $248.45   4.519%   $259.6775   $259.68   $259.70   $259.70  
  Purchase #2 $103.60   8.537%   $112.4443   $112.44   $112.45   $112.40  
  Purchase #3 $102.51   4.107%   $106.7201   $106.72   $106.70   $106.70  
  Purchase #4 $154.45   12.298%   $173.4443   $173.44   $173.45   $173.40  
  Purchase #5 $131.27   3.237%   $135.5192   $135.52   $135.50   $135.50  
  Purchase #6 $34.51   11.303%   $38.4107   $38.41   $38.40   $38.40  
  Purchase #7 $52.93   3.648%   $54.8609   $54.86   $54.85   $54.90  
  7 purchase totals = $827.72       $881.0770   $881.07   $881.05   $881.00