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 $137.90   11.497%   $153.7544   $153.75   $153.75   $153.80  
  Purchase #2 $175.78   10.575%   $194.3687   $194.37   $194.35   $194.40  
  Purchase #3 $167.97   5.807%   $177.724   $177.72   $177.70   $177.70  
  Purchase #4 $152.33   10.216%   $167.892   $167.89   $167.90   $167.90  
  Purchase #5 $107.57   8.828%   $117.0663   $117.07   $117.05   $117.10  
  Purchase #6 $126.70   8.451%   $137.4074   $137.41   $137.40   $137.40  
  Purchase #7 $107.52   3.245%   $111.009   $111.01   $111.00   $111.00  
  7 purchase totals = $975.77       $1,059.2218   $1,059.22   $1,059.15   $1,059.30