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 $161.86   6.107%   $171.7448   $171.74   $171.75   $171.70  
  Purchase #2 $229.70   5.200%   $241.6444   $241.64   $241.65   $241.60  
  Purchase #3 $24.34   11.742%   $27.198   $27.20   $27.20   $27.20  
  Purchase #4 $55.38   12.801%   $62.4692   $62.47   $62.45   $62.50  
  Purchase #5 $230.89   5.150%   $242.7808   $242.78   $242.80   $242.80  
  Purchase #6 $79.54   11.579%   $88.7499   $88.75   $88.75   $88.70  
  Purchase #7 $40.85   6.572%   $43.5347   $43.53   $43.55   $43.50  
  7 purchase totals = $822.56       $878.1218   $878.11   $878.15   $878.00