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 $99.36   10.769%   $110.0601   $110.06   $110.05   $110.10  
  Purchase #2 $94.93   10.425%   $104.8265   $104.83   $104.85   $104.80  
  Purchase #3 $61.76   11.158%   $68.6512   $68.65   $68.65   $68.70  
  Purchase #4 $75.36   5.250%   $79.3164   $79.32   $79.30   $79.30  
  Purchase #5 $119.92   11.730%   $133.9866   $133.99   $134.00   $134.00  
  Purchase #6 $202.98   10.804%   $224.91   $224.91   $224.90   $224.90  
  Purchase #7 $151.97   12.684%   $171.2459   $171.25   $171.25   $171.20  
  7 purchase totals = $806.28       $892.9967   $893.01   $893.00   $893.00