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 $204.33   13.865%   $232.6604   $232.66   $232.65   $232.70  
  Purchase #2 $155.37   12.661%   $175.0414   $175.04   $175.05   $175.00  
  Purchase #3 $57.86   10.713%   $64.0585   $64.06   $64.05   $64.10  
  Purchase #4 $62.29   3.355%   $64.3798   $64.38   $64.40   $64.40  
  Purchase #5 $126.67   3.493%   $131.0946   $131.09   $131.10   $131.10  
  Purchase #6 $174.94   7.365%   $187.8243   $187.82   $187.80   $187.80  
  Purchase #7 $214.53   3.633%   $222.3239   $222.32   $222.30   $222.30  
  7 purchase totals = $995.99       $1,077.3829   $1,077.37   $1,077.35   $1,077.40