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 $68.65   11.556%   $76.5832   $76.58   $76.60   $76.60  
  Purchase #2 $90.71   12.572%   $102.1141   $102.11   $102.10   $102.10  
  Purchase #3 $157.78   4.718%   $165.2241   $165.22   $165.20   $165.20  
  Purchase #4 $166.53   12.478%   $187.3096   $187.31   $187.30   $187.30  
  Purchase #5 $215.85   13.784%   $245.6028   $245.60   $245.60   $245.60  
  Purchase #6 $247.41   8.216%   $267.7372   $267.74   $267.75   $267.70  
  Purchase #7 $48.61   5.778%   $51.4187   $51.42   $51.40   $51.40  
  7 purchase totals = $995.54       $1,095.9897   $1,095.98   $1,095.95   $1,095.90