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 $154.66   8.363%   $167.5942   $167.59   $167.60   $167.60  
  Purchase #2 $148.80   8.653%   $161.6757   $161.68   $161.70   $161.70  
  Purchase #3 $157.31   6.104%   $166.9122   $166.91   $166.90   $166.90  
  Purchase #4 $191.84   5.647%   $202.6732   $202.67   $202.65   $202.70  
  Purchase #5 $126.32   10.343%   $139.3853   $139.39   $139.40   $139.40  
  Purchase #6 $39.69   10.526%   $43.8678   $43.87   $43.85   $43.90  
  Purchase #7 $102.25   10.393%   $112.8768   $112.88   $112.90   $112.90  
  7 purchase totals = $920.87       $994.9852   $994.99   $995.00   $995.10