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 $206.35   13.593%   $234.3992   $234.40   $234.40   $234.40  
  Purchase #2 $207.88   13.320%   $235.5696   $235.57   $235.55   $235.60  
  Purchase #3 $12.29   12.352%   $13.8081   $13.81   $13.80   $13.80  
  Purchase #4 $126.31   8.178%   $136.6396   $136.64   $136.65   $136.60  
  Purchase #5 $171.79   8.505%   $186.4007   $186.40   $186.40   $186.40  
  Purchase #6 $129.56   4.455%   $135.3319   $135.33   $135.35   $135.30  
  Purchase #7 $103.85   12.254%   $116.5758   $116.58   $116.60   $116.60  
  7 purchase totals = $958.03       $1,058.7249   $1,058.73   $1,058.75   $1,058.70