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 $145.87   11.216%   $162.2308   $162.23   $162.25   $162.20  
  Purchase #2 $229.47   3.651%   $237.8479   $237.85   $237.85   $237.80  
  Purchase #3 $41.64   4.183%   $43.3818   $43.38   $43.40   $43.40  
  Purchase #4 $22.73   13.269%   $25.746   $25.75   $25.75   $25.70  
  Purchase #5 $167.80   9.459%   $183.6722   $183.67   $183.65   $183.70  
  Purchase #6 $5.78   8.837%   $6.2908   $6.29   $6.30   $6.30  
  Purchase #7 $126.59   8.230%   $137.0084   $137.01   $137.00   $137.00  
  7 purchase totals = $739.88       $796.1779   $796.18   $796.20   $796.10