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 $175.56   9.516%   $192.2663   $192.27   $192.25   $192.30  
  Purchase #2 $8.96   12.158%   $10.0494   $10.05   $10.05   $10.00  
  Purchase #3 $155.92   13.605%   $177.1329   $177.13   $177.15   $177.10  
  Purchase #4 $138.42   8.604%   $150.3297   $150.33   $150.35   $150.30  
  Purchase #5 $106.85   6.392%   $113.6799   $113.68   $113.70   $113.70  
  Purchase #6 $152.99   4.756%   $160.2662   $160.27   $160.25   $160.30  
  Purchase #7 $26.27   7.537%   $28.25   $28.25   $28.25   $28.30  
  7 purchase totals = $764.97       $831.9744   $831.98   $832.00   $832.00