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 $228.58   10.820%   $253.3124   $253.31   $253.30   $253.30  
  Purchase #2 $193.72   9.736%   $212.5806   $212.58   $212.60   $212.60  
  Purchase #3 $174.44   11.428%   $194.375   $194.38   $194.40   $194.40  
  Purchase #4 $32.60   6.780%   $34.8103   $34.81   $34.80   $34.80  
  Purchase #5 $241.95   12.363%   $271.8623   $271.86   $271.85   $271.90  
  Purchase #6 $236.65   12.151%   $265.4053   $265.41   $265.40   $265.40  
  Purchase #7 $126.67   8.263%   $137.1367   $137.14   $137.15   $137.10  
  7 purchase totals = $1,234.61       $1,369.4826   $1,369.49   $1,369.50   $1,369.50