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 $113.92   6.128%   $120.901   $120.90   $120.90   $120.90  
  Purchase #2 $240.87   4.684%   $252.1524   $252.15   $252.15   $252.20  
  Purchase #3 $43.61   6.677%   $46.5218   $46.52   $46.50   $46.50  
  Purchase #4 $207.29   11.445%   $231.0143   $231.01   $231.00   $231.00  
  Purchase #5 $45.66   12.219%   $51.2392   $51.24   $51.25   $51.20  
  Purchase #6 $151.65   10.573%   $167.684   $167.68   $167.70   $167.70  
  Purchase #7 $23.62   8.379%   $25.5991   $25.60   $25.60   $25.60  
  7 purchase totals = $826.62       $895.1118   $895.10   $895.10   $895.10