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 $211.29   9.221%   $230.7731   $230.77   $230.75   $230.80  
  Purchase #2 $198.59   6.283%   $211.0674   $211.07   $211.05   $211.10  
  Purchase #3 $61.25   7.542%   $65.8695   $65.87   $65.85   $65.90  
  Purchase #4 $90.29   9.169%   $98.5687   $98.57   $98.55   $98.60  
  Purchase #5 $219.92   12.470%   $247.344   $247.34   $247.35   $247.30  
  Purchase #6 $53.42   7.709%   $57.5381   $57.54   $57.55   $57.50  
  Purchase #7 $152.86   8.555%   $165.9372   $165.94   $165.95   $165.90  
  7 purchase totals = $987.62       $1,077.0980   $1,077.10   $1,077.05   $1,077.10