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 $56.98   12.164%   $63.911   $63.91   $63.90   $63.90  
  Purchase #2 $120.56   3.440%   $124.7073   $124.71   $124.70   $124.70  
  Purchase #3 $182.55   11.112%   $202.835   $202.84   $202.85   $202.80  
  Purchase #4 $81.71   6.813%   $87.2769   $87.28   $87.30   $87.30  
  Purchase #5 $211.52   12.174%   $237.2704   $237.27   $237.25   $237.30  
  Purchase #6 $59.84   3.608%   $61.999   $62.00   $62.00   $62.00  
  Purchase #7 $108.85   4.228%   $113.4522   $113.45   $113.45   $113.50  
  7 purchase totals = $822.01       $891.4518   $891.46   $891.45   $891.50