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 $53.25   6.552%   $56.7389   $56.74   $56.75   $56.70  
  Purchase #2 $240.87   9.705%   $264.2464   $264.25   $264.25   $264.20  
  Purchase #3 $152.93   8.125%   $165.3556   $165.36   $165.35   $165.40  
  Purchase #4 $126.55   12.392%   $142.2321   $142.23   $142.25   $142.20  
  Purchase #5 $54.68   10.730%   $60.5472   $60.55   $60.55   $60.50  
  Purchase #6 $202.85   12.301%   $227.8026   $227.80   $227.80   $227.80  
  Purchase #7 $195.59   8.334%   $211.8905   $211.89   $211.90   $211.90  
  7 purchase totals = $1,026.72       $1,128.8133   $1,128.82   $1,128.85   $1,128.70