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 $174.60   10.767%   $193.3992   $193.40   $193.40   $193.40  
  Purchase #2 $38.75   7.566%   $41.6818   $41.68   $41.70   $41.70  
  Purchase #3 $204.25   5.650%   $215.7901   $215.79   $215.80   $215.80  
  Purchase #4 $82.70   3.446%   $85.5498   $85.55   $85.55   $85.50  
  Purchase #5 $54.74   3.537%   $56.6762   $56.68   $56.70   $56.70  
  Purchase #6 $152.26   5.144%   $160.0923   $160.09   $160.10   $160.10  
  Purchase #7 $234.38   8.593%   $254.5203   $254.52   $254.50   $254.50  
  7 purchase totals = $941.68       $1,007.7097   $1,007.71   $1,007.75   $1,007.70