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 $57.34   11.372%   $63.8607   $63.86   $63.85   $63.90  
  Purchase #2 $147.54   11.866%   $165.0471   $165.05   $165.05   $165.00  
  Purchase #3 $225.87   9.204%   $246.6591   $246.66   $246.65   $246.70  
  Purchase #4 $200.95   5.733%   $212.4705   $212.47   $212.45   $212.50  
  Purchase #5 $191.30   10.628%   $211.6314   $211.63   $211.65   $211.60  
  Purchase #6 $207.45   3.424%   $214.5531   $214.55   $214.55   $214.60  
  Purchase #7 $95.82   4.585%   $100.2133   $100.21   $100.20   $100.20  
  7 purchase totals = $1,126.27       $1,214.4352   $1,214.43   $1,214.40   $1,214.50